题目内容
3层混凝土强度等级()。
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Which of the following statements is TRUE according to the passage？
小蜂窝可先用水冲洗干净，用()水泥砂浆修补。
Traditional thinking up to now has been that the distinctive, upright body form. of modern humans has come about as a result of the ability to walk, and that running is simply a by-product of walking. Furthermore, humans have usually been regarded as poor runners compared to such animals as dogs, horses or antelopes. However, this is only true if we consider fast running, or sprinting, over short distances. Even an Olympic athlete can hardly run as fast as a horse can gallop, and can only keep up a top speed for fifteen seconds or so. Horses, antelopes and greyhounds, on the other hand, can run at top speed for several minutes, clearly outperforming us in this respect. But when it comes to long-distance running, humans do astonishingly well. They can maintain a steady pace for miles, and their overall speed compares favourably with that of horses or dogs.
Bramble and Lieberman examined twenty-six anatomical features found in humans. One of the most interesting of these is the nuchal ligament, a band of tissue that extends from a ridge on the base of the skull to the spine. When we run, it is this ligament that prevents our head from pitching back and forth or from side to side. Therefore, we are able to run with steady heads, held high. The nuchal ligament is not found in any other surviving primates, although the fossil record shows that Homo erectus, an early human species that walked upright, much as we do, also had one. Then there are our Achilles tendons at the backs of our legs, which connect our calf muscles to our heel bones -- and which have nothing to do with walking. When we run, these tendons behave like springs, helping to propel us forward. Furthermore, we have low, wide shoulders, virtually disconnected from our skulls, another anatomical adaptation which allows us to run more efficiently. Add to this our light forearms, which swing out of phase with the movement of our legs to assist balance, and one begins to appreciate the point that Bramble and Lieberman are trying to make.
But what evolutionary advantage is gained from being good long-distance runners？ One hypothesis is that this ability may have permitted early humans to obtain food more effectively. "What these features and fossil facts appear to be telling us is that running evolved in order for our direct ancestors to compete with other carnivores for access to the protein needed to grow the big brains that we enjoy today," says Lieberman.
The human ability to run ______.
对混凝土的较大、较深裂缝用水泥浆修补时，总厚度控制在()，并压实抹光。
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