流行性出血热的传染源是()
A.患者
B.宿主动物
C.蚊虫
D.苍蝇
E.黑猩猩
参考答案:B
It is reported that fully 95 per cent of ____ US public schools are now connected to ____ Internet.
简述永磁直流伺服电动机的组成、特点及工作原理。