下列细菌中,对人类有害的是 [ ]
A.乳酸细菌
B.甲烷菌
C.肺炎双球菌
D.根瘤菌
答案:C
The government work report by Premier Wen covers a variety of issues, and the prices of agricultural products ______.
A.in common
B.in general
C.in particular
D.in practice
用天然气灶烧水,燃烧0.5m3的天然气,使100kg的水从20℃升高50℃.已知,水的比热容c=4.2×103J/(kg·℃),天然气的热值q=7.0×107J/m3.求:
(1)0.5m3天然气完全燃烧放出的热量Q放.
(2)水吸收的热量Q吸.
(3)燃气灶的效率η.