All the students injured in that accident are still in hospital, ________for further observation. [ ]

A. kept  

B. keeping

C. having kept  

D. to be kept

对于渗透系数大、地下水丰富的软土地基，人工降低地下水位宜采用（）。

A.管井法 

B.真空井点法 

C.喷射井点法 

D.电渗井点法