### part 1 ###
%s/a//

### part 2 ###
2,10d
10,$s/Cat/Dog/g

### part 3 ###
0,10s/o/u/g
11,20s/i/j/g
0,$d

### part 4 ###
5,12s/[a-z]/t/g

### part 5 ###
%s/a//g