Having a trip abroad is certainly good for the old couple,but it remains__whether they will enjoy iA to seeB seeingC to be seenD seen
问题描述：
Having a trip abroad is certainly good for the old couple,but it remains__whether they will enjoy i
A to see
B seeing
C to be seen
D seen
答
C it 是see 的逻辑主语 it指代出国旅行这件事 那么出国旅行自己不能看 所以用被动。
而remain 后面加形容词或动词不定式。所以这里既是被动又是不定式，因此用动词不定式的被动形式。
答
C remain to do sth加被动
答
it remains to be seen
固定用法
无法确定某事未来发生或者发生了的
答
A
答
C
一次国外旅行对这对老夫妇肯定是有好处的,但是他们能不能喜欢这次旅行尚待观察.
see这个动作是别人发出的,换句话说是被动句.