题目内容：

高一英语非谓语动词 高手请进
whether----,we will have a picnic tomorrow.
A.permit B.permits C.permitted D.permitting
----carefully,this letter is very beautiful.
A,type B.typing C.typed D.to typed
请问什么时候用过去分词,什么时候用-ING形式?谢谢