当遇到难题时，我们可以（   ）

①先独立思考   ②找合适的时间与同学探讨

③向老师请教   ④知难而退

A．②③

B．①②③

C．①③

D．①②③④

--- 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