--- Are your family ready for rafting?

---Yes, I really want my children to experience that       they are young 

A．\

B．while

C．unless

D．if

隧道衬砌使用的水泥不宜采用（）水泥。

A、硅酸盐水泥

B、普通硅酸盐水泥

C、早强水泥