Is ____ dangerous to swim in the river alone?

A．it

B．this

C．that

D．he

重力式码头干地填土的填料应分层压实，每层填土虚铺厚度，对机械夯实或辗压不宜大于()。

A.0.2m 

B.0.3m 

C.0.4m 

D.0.5m