简单英语小疑问,有关动词

题目

简单英语小疑问,有关动词
动词在开头何时要用”＋ing”形式?
比如：记住它．就是remember it.
可是：订购东西不会花费你太多时间．就是”ordering things won't take you much time.
为什么一会儿用"+ing"形式,一会不用?有何规律?

答案

remember it是口语,可看作是省略句,例如；you should remember it.
ordering things won't take you much .中ordering是动名词,在句子中作主语.相当于名词一样.