1．He studies by listening to tapes for a test．（就划线部分提问）

                  he          for a test?

2．My sister had long hair in the past, but now she has short hair．（同义句转换）

My sister                                    long hair．

3．Teachers should allow us to do homework with friends．（同义句转换）

We should                      to do homework with friends．

4．It must be Carla's．（同义句转换）

It must                   Carla．