ought to do sth 的否定
devoteto后面是do还是doing
leave sb. to do sth.什么意思
devote oneself to doing
devote oneself to do还是doing
ask sb. to do sth.什么意思
come together to do sth意思
offer sb sth和offer sth to sb
help sb to do sth造句
sth be used to do sth 例句