N20的中枢系统作用,正确的是()
A.吸入30%~50%有镇痛作用
B.吸入>30%有麻醉作用
C.降低颅内压
D.增加脑血流
E.麻醉作用极强
参考答案:A
Helen has had a lot of trouble these days,but she doesn’t know whom to ______ for help.
A.turn to
B.look for
C.deal with
D.talk about
带电作业前为什么要进行现场勘察?勘察工作有哪些内容?