为什麽英语今晚的动词要加ing形式

1.I'm visiting my friends.2.He isn't writing a postcard.3.Is she enjoying her visit?4.Are they buying postcards?动名词形式也要加（动名词即是具有名词性质的动词）eg：Making the bed is very simple!这里的“making"不是做（动词），而是一个名词还有现在进行时也要加"ing"，一般情况下系动词（am is are)不能和动词同时出现，要在动词后加“ing”.I'm visiting my friends. 是将来时visit是一个瞬间动词作一般现在时没“ing”形式。He isn't writing a postcard是现在进行时意为：他没在写明信片。.Is she enjoying her visit? 一般情况下系动词（am is are)不能和动词同时出现，要在动词后加“ing”.Are they buying postcards? 是现在进行时意味：他们正在买明信片吗？o(*￣︶￣*)o希望我的答案能帮到你！！^_^