通报的表达方式侧重于（）。A.叙事 B.说理 C.说明 D.说明、说理

在“用打点计时器测速度”的实验中，打点计时器应接______（直流或交流）电源．如果电源的频率是50Hz，它每隔______s打一个点．在某次实验中，舍去打出的纸带前面比较密集的点，从0点开始，每5个连续点取1个计数点，标以0、1、2、3…那么相邻两个计数点之间的时间为______s．

—Thank God. It's Friday again. A nice weekend.

一_______. [ ]

A.  Me too

B. Yes, I'll be free then

C. That's all right

D. The same to you

男性，34岁，突然上腹部疼痛6小时，呈刀割样疼痛，迅速波及全腹，伴恶心，呕吐。查体：腹肌紧张，呈板样硬，全腹有压痛和反跳痛，肠鸣音消失，最可能的诊断是

A．左半结肠癌
B．右半结肠癌
C．小肠肿瘤
D．克罗恩病
E．溃疡性结肠炎

腹部压痛示急性胆囊炎（）

A.McBumey点压痛

B.MurPhy征阳性

C.中上腹压痛

D.脐周压痛

E.下腹正中压痛

One-fifth of the light switches produced by a certain factory are defective. Four-fifths of the defective switches are rejected and

of the nondefective switches are rejected by mistake. If all the switches not rejected are sold, what percent of the switches sold by the factory are defective