题目内容：

We had to stop to have a rest,_____we were very tired
A while
B when
C whether
D because

优质解答

D
stop to do sth表示停下来去做某事
前半句意思是：我们不得不停下来去休息
后半句：我们很累
所以用because
整句的意思：我们不得不停下来去休息因为我们很累