問題詳情

In diet-obsessed America, it’s hard to say an encouraging word about lipids—a term biochemists use to includeall fats and oils. Yet life would be utterly impossible without them. Cell membranes, as we have seen, depend criticallyon a two-ply lipid layer to keep out unwanted elements. The insulating sheaths of nerve cells are built from fats, whichis one reason why growing babies with rapidly developing nervous systems need a fair amount of fat—and why breastmilk contains so much of it. Fat makes up only 12 percent of a newborn’s weight, but increases to nearly 30 percent bythe end of a child’s first year. Fats also help generate a number of important hormones collectively calledsteroids—compounds structurally related to cholesterol—such as estrogen and testosterone. Of course, they also makeeffective padding to keep you warm and to cover vulnerable body parts such as the kidneys.Although physicians recommend that adults rely on lipids for no more than 20 percent of their daily intake, mostAmericans eat a lot more fat—chiefly from meat, eggs, cheese, assorted fried “junk foods,” and various plant sourcessuch as nuts, peanut butter, and vegetable oils. Dietitians now recommend that men have 15 percent body fat byweight, and women no more than 20 percent, although social custom has dictated spectacularly different ratios over thecenturies. Many cultures have regarded female plumpness as a sign of fertility—for the excellent reason thatconspicuous body fat suggests that a woman has a good supply of nutrients to feed a fetus and nurse a newborn.
37 What is the main idea of the first paragraph?
(A) Americans work hard to rid themselves of fat.
(B) Fat is vital to our nervous system.
(C) Fats help generate a number of important hormones.
(D) Fat is an essential part of life.

參考答案

答案：D
難度：適中0.4
統計：A(5),B(18),C(15),D(28),E(0)

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