The children climed to the top of the hill,____ they picniced.

问题描述:

The children climed to the top of the hill,____ they picniced.
A.in which B.on that C.allowed D.agreed
书上给的答案是C,可是怎么翻译,

孩子们爬上山的顶峰,他们被允许在(山上)野餐.
A 如果改成on which就对了,因为只能是on the hill
B that前一般不能加介词
D 应该是agree to do