N0的麻醉禁忌证有()
A．低温体外循环麻醉
B．空气栓塞
C．气胸
D．肠梗阻
E．严重休克和危重病人
参考答案：B, C, D, E
进行有性生殖的生物，子代与亲代之间存在着一定差异的主要原因是[ ]
A．基因重组
B．染色体发生变异
C．基因突变
D．生活条件的改变
When they retire, many people over 60 prefer the houses in the country to spend their remaining years to __________ in a large city.
A．it
B．that
C．those
D．which
