为减少随机误差，除必须严格控制实验条件、正确执行操作规程外，还可用增加（）。 A.样

制备无菌空气时，介质纤维直径越小，过滤效率（）

A、越低

B、越高

C、没有直接关系

D、根据情况而定

合同法律关系的主体是参加合同法律关系，享有相应权利，承担相应义务的当事人。下列主体中，可以作为合同法律关系主体的有（）。

A.政府机关

B.法人的分支机构

C.大学所属二级学院

D.事业单位

E.社会团体

电子束的危害性有（）。

A.易损伤视觉

B.灼伤伤害

C.易受高频磁场危害

D.r射线伤害

E.x射线伤害

When Dave was eighteen, he bought a secondhand car for 200 so that he could travel to and from work more (1) than by bus. It worked quite well for a few years, but then it got so old, and it was costing him (2) much in repairs that he decided that he had better (3) it.

He asked among his friends to see if anyone was particularly (4) to buy a cheap car, but they all knew that it was falling to pieces, so (5) of them had any desire to buy it. Dave’s friend Sam saw that he was (6) when they met one evening, and said, "What’s (7) , Dave"

Dave told him, and Sam answered, "Well, what about advertising it in the paper You may (8) more for it that way than the cost of the advertisement!" Thinking that Sam’s (9) was sensible, he put an advertisement in an evening paper, which read "For sale: small car, (10) very little petrol, only two owners. Bargain at 50. " For two days after the advertisement first appeared, there was no (11) . But then on Saturday evening he had an enquiry. A man rang up and said he would like to (12) him about the car. "All right, " Dave said, feeling happy. He asked the man whether ten o’clock the next morning would be (13) or not. "Fine, " the man said, "and I’ll (14) my wife. We intend to go for a ride in it to (15) it. "

The next morning, at a quarter to ten, Dave parked the car in the square outside his front door, (16) to wait there for the people who had (17) his advertisement. Even Dave had to (18) that the car really looked like a wreck. Then, soon after he had got the car as clean (19) it could be, a police car stopped just behind him and a policeman got out. He looked at Dave’s car and then said, "Have you reported this (20) to us yet, sir\

17().

A.read 

B.inserted 

C.answered 

D.placed

外感风湿所致头痛是

A．胀痛
B．隐痛
C．刺痛
D．重痛