difficulty doing sth造句
difficultydoingsth是什么意思
have difficulty doing sth
have difficulty doing用单数还是复数
have difficulty to do还是doing
cant help doing sth是什么意思
cant stop doing sth是什么意思
waste time to do 还是doing sth
prevent sb from doing sth是什么意思
stoptodosth和stopdoingsth的区别
employ oneself in doing sth例句