Choose the underlined part A,B,C or D that needs correcting

Choose the underlined part A,B,C or D that needs correcting
1.For some young people enjoyment involves sittingin front a computer playing games
     A                                                 B               C                                               D
2. His parent are thinking of banning him on using the computer
                              A         B             C    D
3. When you game online, be carefully when making friends with strangers
                       A                        B                         C                   D