2023年3月英语六级真题答案（第1套）

The suggestion that people should aim for dietary diversity by trying to eat a variety of foods has been a basic public health recommendation for decades in the United States and elsewhere. Now, however, experts are warning that aiming for a diverse diet may actually lead to just eating more calories, and, thus, to obesity. One issue is that people may not interpret "variety" the way nutritionists intend. This problem is highlighted by new research conducted by the American Heart Association. Researchers reviewed all the evidence published related to dietary diversity and saw a correlation between dietary diversity and a greater intake of both healthy and unhealthy foods. This had implications for obesity, as researchers found a greater prevalence of obesity amongst people with a greater dietary diversity.

One author of the new study explained that their findings contradict standard dietary advice, as most dietary guidelines around the world include a statement of eating a variety of foods. But this advice does not seem to be supported by science, possibly because there is little agreement about the meaning of "dietary diversity, which is not clearly and consistently defined. Some experts measure dietary diversity by counting the number of food groups eaten, while others look at the distribution of calories across individual foods, and still others measure how different the foods eaten are from each other.

Although the findings of this new study contradict standard dietary advice, they do not come as a surprise to all of the researchers involved. Dr. Rao, one of the study authors, noted that, after 20 years of experience in the field of obesity, he has observed that people who have a regimented lifestyle and diet tend to be thinner and healthier than people with a wide variety of consumption. This anecdotal evidence matches the conclusions of the study, which found no evidence that dietary diversity promotes healthy body weight or optimal eating patterns, and limited evidence shows that eating a variety of foods is actually associated with consuming more calories, poor eating patterns and weight gain. Further, there is some evidence that a greater variety of food options in a single meal may delay people's feeling of fullness and actually increase how much they eat.

Based on their findings, the researchers endorse a diet consisting of a limited number of healthy foods such as vegetables, fruits, grains, and poultry. They also recommend that people simultaneously endeavor to restrict consumption of sweets, sugar and red meat. The researchers stress, however, that their dietary recommendations do not imply dietary diversity is never positive, and that, in the past, diversity in diets of whole, unprocessed food may have actually been very beneficial.

The ability to make inferences from the same and different, once thought to be unique to humans, is viewed as a cornerstone of abstract intelligent thought. A new study, however, has shown that what psychologists call same-different discrimination is present in creatures generally seen as unintelligent: newborn ducklings (小鸭).

The study, published Thursday in Science, challenges our idea of what it means to have a birdbrain, said Edward Wasserman, an experimental psychologist at the University of Iowa who wrote an independent review of the study.

"In fact, birds are extremely intelligent and our problem pretty much lies in figuring out how to get them to 'talk' to us, or tell us how smart they really are," he said.

Antone Martinho and Alex Kacelnik, co-authors of the new paper, devised a clever experiment to better test bird intelligence.

First, they took 1-day-old ducklings and exposed them to a pair of moving objects. The two objects were either the same or different in shape or color. Then they exposed each duckling to two entirely new pairs of moving objects.

The researchers found that about 70% of the ducklings preferred to move toward the pair of objects that had the same shape or color relationship as the first objects they saw. A duckling that was first shown two green spheres, in other words, was more likely to move toward a pair of blue spheres than a mismatched pair of orange and purple spheres.

Ducklings go through a rapid learning process called imprinting shortly after birth—it's what allows them to identify and follow their mothers.

These findings suggest that ducklings use abstract relationships between sensory inputs like color, shape, sounds and odor to recognize their mothers, said Dr. Kacelnik.

By studying imprinting, the authors of this study have shown for the first time that an animal can learn relationships between concepts without training, said Jeffrey Katz, an experimental psychologist at Auburn University who was not involved in the study.

Previous studies have suggested that other animals, including pigeons, dolphins, honeybees and some primates (灵长类动物), can discern same from different, but only after extensive training.

Adding ducklings to the list- particularly untrained newborn ducklings -- suggests that the ability to compare abstract concepts "is far more necessary to a wider variety of animals' survival than we previously thought," Dr. Martinho said. He believes the ability is so crucial because it helps animals consider context when identifying objects in their environment.

It's clear from this study and others like it that "animals process and appreciate far more of the intricacies in their world than we've ever understood," Dr. Wasserman said. "We are in a revolutionary phase in terms of our ability to understand the minds of other animals."