【单选题】
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 head is down) to the heart. How come giraffes don’t black out when they drink
The answer to the{{U}} (77) {{/U}} feet problem, the researchers found, is that giraffes have{{U}} (78) {{/U}} the researchers call a "natural anti-gravity suit". It{{U}} (79) {{/U}} out that the skin and other{{U}} (80) {{/U}} in their legs and feet are{{U}} (81) {{/U}} stiffer and tougher than those of other{{U}} (82) {{/U}} .As a result, the blood vessels in the leg cannot swell.
Therefore, the blood has nowhere to go but back to the heart. What about blood rushing to the head{{U}} (83) {{/U}} the giraffe bends down to drink The researchers found that the giraffe’s jugular vein, which{{U}} (84) {{/U}} blood from the head back to the heart, has lots of one-way valves in it. In the giraffe’s neck, there are lots of muscles that flex and relax repeatedly as the animal moves its head and sucks{{U}} (85) {{/U}} drinking water.By squeezing the valved jugular vein, they{{U}} (86) {{/U}} blood moving back to the heart even while the animal is drinking.
B．where
C．that
D．those
网考网参考答案：A
网考网解析：
语法结构题。空格为所在句子从句的引导词，在从句中作宾语，所以A正确。 document.getElementById("warp").style.display="none"; document.getElementById("content").style.display="block"; 查看试题解析出处>>
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