每个采煤工作面必须至少有（）个畅通无阻的安全出口。
A.1
B.2
C.3
D.4
参考答案：B
---He hasn’t tried Amazon Buffet before, has he? ---______. He hopes to have a chance to eat there.
A．No, he has
B．No, he hasn’t
C．Yes, he has
D．Yes, he hasn’t
棉株茎部叶片对肥、水反应很敏感，它们的色泽、空间排列位置和顶芽的肥瘦常作为田间（）指标。
