it 复数（they） colour动词（colour） these单数（this）
1.the trees are green.对green提问
What colours are the trees?
2.these are blue flowers（改为同义句子）
These flowers are blue
3.Is the car black?否定回答
No,it isn't
4.this bag is yellow 改为复数句子
These bags are yellow
5.what colour is the book?改为复数句子
What colours are the books?