如图所示，AB是一质量为m的均匀细直杆，A端靠在光滑的竖直墙壁上，B端置于水平地

His dog did everything he told it to do. ___ a most obedient animal.

A．It is

B．It were

C．It are

D．It was

热汽对流锅，也叫高压蒸汽锅。

按苷键构型将苷分为( )

A．C-苷，S-苷，O-苷，N-苷
B．原生苷，次生苷
C．单糖链苷，双糖链苷等
D．单糖苷，双糖苷等
E．α-苷，β-苷

施工电梯底笼周围（）范围内必须设置牢固的防护栏杆。

A.2.5m

B.3.0m

C.4.0m

D.5.0m

演讲稿实质上就是一种特殊的应用文。