电凝止血的原理是______________________。
参考答案:电热作用使血液凝结
一节干电池的电压为______,实验室用三节蓄电池串联成的蓄电池组的电压为______,我国照明电路的电压为______,人体安全电压为______.
You can’t shut your eyes to the fact ______more than 20% of American Families now live below the poverty line.
A.what
B.which
C./
D.that