1.____(come) at 4o'clock if the plane arrives on time.
2.I didn't go shopping this morning as I ___(do)the housework.
3.She___(come)to see me yesterday,but she forgot.
4.You___(ask)for permission before you left the table.
5.As they didn't understand,I ___(explain)everything again.
用should,ought to和have to来填空!