1.They knew everything only after you told them
they knew nothing before you told them
2.Because of SARS,he didn't take a trip to Guangzhou.Hestayed at home.
He stayed at home instead of taking a trip to Guangzhou because of SARS.
3.There aren't any pears in the box
There are no pears in the box
4.She like singing better than dancing.
She prefers singing to dancing
5.My sister is not old enough to join the army.
My sister is too young to join the army.
6.Shall we go for a picnic tomorrow?
Why not go for a picnic tomorrow?
7.John will go bed after he finishes his homework.
John won't go tobed until he finishes his homework.