当to在句中呈现介词的时候会跟doing形式.比如 ：
I am looking forward to hearing from you.
Many people prefer spending money to earning money.
Going to a concert is great alternative to going to dinner.
I am used to eating rice now.
等等用法,但是归根究底因为这些句子当中to是介词,而不是动词不定时
帮忙总结一下高中英语中to+doing的结构 ,