眼力大比拼！找出错误并在横线上改正。

( ) 1. Can you help washing the dishes?                                          

                           A       B               C

( ) 2. My family live in a house.                                                      

                     A      B   C

( ) 3. Let's put a circle at usually.                                                       

                      A B         C

( ) 4. How many class are there in your school?                               

               A      B      C

采用人工挖孔时，挖孔作业人员下班休息必须盖好孔口，或设高于（）厘米的护身栏封闭围住

A.50

B.80

C.120