从下面各句A、B、C、D中找出一处错误并改正。

1. That's a chinese car.                                           

       A    B     C       D

2. That is a pencil box.                                            

      A   B C       D

3. — What's this in English?                                     

            A        B 

    — It's computer.                                                 

          C       D

4. — And what's this?                                              

          A       B     C

    — This is a pencil sharpener.                                 

            D

如何防止井下火源？