英语这3道选择题好难怎么写?

英语这3道选择题好难怎么写?
1,—Why do you look sad?
—There are so many problems _____.
A.remaining to settle
B.remained settling
C.remaining to be settled
D.remained to be settled
2,She will tell us why she feels so strongly that each of us has a role _________in making the earth a better place to live．
A.to have played
B.to play
C.to be played
D.to be playing
3,Having a trip abroad is certainly good for the old couple,but it remains_________ whether they will enjoy it．
A.to see
B.to be seen
C.seeing
D.seen