锅炉停炉熄火通风结束后，锅炉各处人孔门检查孔及风门档板应（）。
A.全部开启
B.全部关闭
C.稍微开启
D.风门开启，人孔门、检查孔关闭。
参考答案：B
能引起可遗传的变异的一项是：[ ]
A．个体生长太快
B．遗传物质发生了变化
C．个体发育太好
D．生存环境发生了变化
—Have you seen Dr. Adams recently?
—No. He __________ Hong Kong for an international meeting. He’ll come back tomorrow.[ ]
A. has gone in
B. has been in
C. has gone to
D. has been to
