问题

There are so many tall trees in the forest, ______ .
A:some of them measures 50 metres
B:some of which measuring 50 metres
C:some of them measuring 50 metres
D:some of which measures 50 metres
B:some of which measuring 50 metres
C:some of them measuring 50 metres
D:some of which measures 50 metres
正确答案是: