After the hard work, they were tired ________happy.[ ]
A. so
B. with
C. but
答案:C
B.电源的电动势在数值上等于两极间的电压
C.电源的电动势与电压的单位相同,但与电压有本质的区别
D.电动势越大,电源两极间的电压一定越高
不直接引起发热而由内热源引起的是()。
A.白细胞
B.病原微生物