英语语法be动词问题

英语语法be动词问题
选择正确的答案填空：
1.This postcard () great!(is,are)
Yes,().(it is,they are)
2.These stamps () beautiful!(is,are)
Yes,().(it is,they)
3.How big () they?(is,are)
4.How long () it?(is,are)
5.() a map of China,(It's,They're)
6.() a picture of the Great Wall.(It's,They're)