沸腾炉中受热面的（）虽很高，但炉堂上部（）的传热量却比一般煤粉锅炉的低。
参考答案：传热强度、悬浮段
I asked him ___ it, but he just remained unmoved.
A．how to do
B．to do
C．how doing
D．doing
----Why didn’t you tell me about the meeting?
----I ______ tell you the day before yesterday. You just forget it.
A．do
B．did
C．had to
D．must
