什么情况下动词前加ing?

how about doing sth; what about doing sth; be busy doing sth; finish doing sth; feel like doing sth; be afraid of doing sth; be used to doing; look forward to doing sth; listen to doing; enjoy doing sth; like doing sth; avoid doing sth; stop sb from doing; keep sb from dong sth; prevent sb from doing; save sb from doing sth; spend st (in) doing sth……

同楼上，what/how about 加ing

现在进行时
动词变化规则
A、直接+ ing
B、去e+ing
C、重读闭音节，且末尾只有1个辅音字母，双写辅音字母+ing
D、特殊变化：die-dying, lie-lying，tie-tying
E、不规则变化