He was unable to make such progress, __________________.

A．as he tried hard

B．as hard he tried

C．so hard did he try

D．hard as he tried

硅酸盐水泥水化产物中，对水泥石的粘结力和强度起主要作用的是（）。

A．水化铝酸钙

B．水化硅酸钙

C．水化铁酸钙

D．氢氧化钙