选出句中的错误并改正。

( ) 1. I usually walks to school.                                        

                  A        B     C  

( ) 2. I'm going to playing the guitar.                                 

                     A    B     C 

( ) 3. I have much dresses.                                               

                 A      B        C

( ) 4. I want singing a song.                                              

                           A    B   C

( ) 5. Are you always do your homework?                          

              A            B      C

网络安全的定义和目标是什么？