流沙地段施工首先应制止水夹泥沙涌入坑道，施工需用( )的方法。
A．先护后挖
B．互挖结合
C．灌浆封堵
D．密闭支撑
E．边挖边封
参考答案：A,D,E
It's a common _______ for young people to pay a New Year's visit to their elders.
A．sense
B．practice
C．rule
D．scene
吸附热分为积分吸附热和（）
