Having a trip abroad is good for the old couple,but it remains seeing whether they will enjoy it.

这是一道高考题目,很老了.
这题的正确答案不是 seeing ,而是to see.
整个句子是这样的:
Having a trip abroad is good for the old couple,but it remains to see whether they will enjoy it.
意思是:
能去出国旅行对于这对老年夫妇来说是好的,但是是否他们能玩得高兴仍然有待于证实.
在这个句子中,
it remains to be seen ……是一个固定短语,表示……有待于观察,有待于证实..那本句用remains to be seen呢？所以本句要用remains to be seen表示"有待于被证实."你回答中的第二句不是说用：to see嘛!从你问的角度说,是用doing 还是to do?所以只能说用to do,但是不定式有不同的时态的语态,所以这里用被动语态.