1.He is writing a letter now.(改为一般疑问句）
Is he writing a letter now?
2.She is going to ride a bike this Sunday.（last Sunday)
She went to ride a bike last Sunday.
3.Kate ran in the park yesterday.（一般现在时）
Kate runs in the park .
4.This is a dog.(改复数句）
This are dogs .
5.This box of tissues is eight yuan(划线部分提问）eight yuan被画
How much is this box of tissues
6.You mustn't talk in class.(祈使句）
Don't talk in class
7.Mrs Black likes fishing and shopping.(改否定句）
Mrs Black doesn't like fishing and shopping
8.Tom runs very quickly.(改感叹句）
How quickly Tom runs !
9.I'm older than my sister.(改同义句）
My sister is younger than me.
10.How much are the dolls?(用￥39回答）
the dolls are ￥39.