当to是介词时，后跟动词要用ing形式。当to是不定式符号时，后用动词原形。to后面接动词原形，构成动词不定式，to后面还可以接动名词，这时to作介系词来使用。
“to”为介词的英语短语
adjust to doing：调整做……
adapt to doing：适应做……
lead to doing：领导做……
the answer to doing
the exit to doing
the entrance to doing
pay attention to doing：集中做
do harm to doing：伤害
say hello to doing：说你好
be similar to doing
