Genetically speaking, there are advantages to avoiding substantial height. During childbirth, larger babies have more difficulty passing through the birth canal. Moreover, even though humans have been upright for millions of years, our feet and back continue to struggle with bipedal posture and cannot easily withstand repeated strain imposed by oversize limbs. “There are some real constraints that are set by the genetic architecture of the individual organism,” says anthropologist William Leonard of Northwestern University.

33. On which of the following statements would the author most probably agree?
[A] Non-Americans add to the average height of the nation.
[B] Human height is conditioned by the upright posture.
[C] Americans are the tallest on average in the world.
[D] Larger babies tend to become taller in adulthood.

【解析】文中第四段第三句的言外之意是，人类身高有其极限，而这个身高极限与直立行走的姿势有关。选项[B]中的conditioned是对原文中struggle with的同义转换。