问题描述：
2.There is a big dog _______to a fence outside the house.
A.tying B.tied C.to tie D .ties
4._______the early train,you'll have to get up early and rush in a taxi.
A.Catching B.Caught C.To catch D.Catch
4为什么不选D?
A.tying B.tied C.to tie D .ties
4._______the early train,you'll have to get up early and rush in a taxi.
A.Catching B.Caught C.To catch D.Catch
4为什么不选D?
问题解答：
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