有个句子it's convenient _something at the supermarket.是填to buy还是

还原后就是buying something at the supermarket is convenient.，，，，到底是选buying还是to buy呢

形式主语应该不都用to do吧

用doing的时候：It is + no use, no good (fun, a great pleasure, a waste of time, a bore...)等名词+doing sth. It is no use crying.哭没有用。It is no good objecting.反对也没有用。 It is a great fun playing football．打篮球很有趣。 It is a waste of time trying to explain．设法解释是浪费时间。