导致脑梗死最常见的病因是（）
A.分水岭脑梗死
B.腔隙性脑梗死
C.短暂性脑缺血发作
D.脑栓塞
E.脑血栓形成
参考答案：E
— Do you think it's a good idea to make friends with your students?
— _____, I do. I think it's a great idea. [ ]
A. Really
B. Obviously
C. Actually
D. Generally
防毒面具的过滤剂有一定的使用时间，一般为30～（）分钟。过滤剂失去过滤作用（面具有特殊气味）时，应及时更换。
A.70
B.80
C.90
D.100
