[单项选择]An adult giraffe’s head is about six feet above its heart. This means that tocenough blood up to the brain the circulatory (68) must be strong enough to keep the blood at very high pressure.
Biologists have known for some time that giraffes solve this problem by having (69) high blood pressure, about (70) that of human beings. But an international team of biologists began to (71) about this. If giraffes havesuch high blood pressure, they should have a (72) problem with swelling in their legs and feet. Why don’t giraffes have swollen feet
Giraffes should have (73) problem, too. Every time they bend heads (74) to drink, the blood should (75) to their heads and have a hard time (76) back up (when the head is down) to the heart. How come giraffes don’t black out when they drink
The answer to the (77) feet problem, the researchers found, is that giraffes have (78) the
A. terrible
B. unreliable
C. unsolvable
D. advisable

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An adult giraffe’s head is about six feet above its heart. This means that to{{U}} (67) {{/U}}enough blood up to the brain the circulatory{{U}} (68) {{/U}}must be strong enough to keep the blood at very high pressure.
Biologists have known for some time that giraffes solve this problem by having{{U}} (69) {{/U}}high blood pressure, about{{U}} (70) {{/U}}that of human beings. But an international team of biologists began to{{U}} (71) {{/U}}about this. If giraffes have such high blood pressure, they should have a{{U}} (72) {{/U}}problem with swelling in their legs and feet. Why don’t giraffes have swollen feet
Giraffes should have{{U}} (73) {{/U}}problem, too. Every time they bend heads{{U}} (74) {{/U}}to drink, the blood should{{U}} (75) {{/U}}to their heads and have a hard time{{U}} (76) {{/U}}back up (when the h
A. bring
B. transfer
C. produce
D. pump

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