并改正过来)1.Is that your skirt?No,that isn't.2.Are you going to

1.Is that your skirt?No,(it) isn't.
对that/this的一般疑问句的回答都是用it代替that/this.
2.Are you going to the bank?Yes,(I am).
单独的I'm不能缩写来回答一般疑问句.
3.Mike (is) watching TV at home now.
现在进行时的句子谓语结构为：be + 动词的现在分词.
4.(Whose) shirt is the best?It 's Tong's.
不能用who's来表示形容词物主代词,应该用whose.
5.This book is (cheaper) than that one.
后面有than,所以用比较级cheaper,不用最高级cheapest.
6.My friends usually (want) to play computer games every day.
every day做时间状语,句子最好使用一般现在时,而不是一般过去时.

3，应加上谓语 is
5 cheapest是最高级，应该用比较级 cheaper
6 usually 是通常的意思是一般现在时态，不能用过去时 wanted

3 Mike is watching TV at home now. 此处缺谓语所以应加is
5 This book is cheaper than that one.两者比较用比较级，而且若用最高级，前面要加the
6 My friens usually want to play computer games every day.在此处有usually 和every day 很...