—What do you think of Paul? —He is frien

—I guess you can buy such a smart phone for 300 dollars.

—I could just two months ago，but the price ________ by 20%.

A．went up

B．had gone up

C．has gone up

D．goes up

增生性龈炎的直接病因是

A．牙菌斑
B．服用药物
C．内分泌导致的激素变化
D．遗传因素
E．全身疾病

采用紫外线消毒手术室空气时，照射距离不超过（）

A.1m

B.2m

C.3m

D.4m

E.5m

哪些情况允许对不停电设备的继电保护停用检查或试验？

夜间行车前方遇到这种情况时不能盲目让超。