下列物质溶于水,所得溶液的pH大于7的是 [ ]
A.干冰
B.生石灰
C.食醋
D.食盐
答案:B
瞳孔扩大是由下列哪种神经调节的
A.副交感神经B.交感神经C.视神经D.展神经E.三叉神经
The height of a VHF radio antenna is more important than the power output wattage of the radio because().
A.VHF communications are basically line of sight
B.the air is more dense the higher you go
C.salt water is a poor conductor of sound
D.sea water absorbs the radiated energy