下列选项中，不属于蒸汽热网的是( )。
A．高压热网B．低压热网C．中压热网D．一级管网
参考答案：D
涂料的备案申请在涂料进口至少( )个月前向备案机构提出。
A．1
B．2
C．3
D．6
(2013·济南二模)It was during the Ming Dynasty ________ the Great Wall was repaired and extended to take on the appearance it has today.
A．when
B．which
C．what
D．that
