求英语帮忙

书上例子
第一句：There were small desks in the classroom before. 以前教室有小桌子
第二句：There are big desks in the classroom now. 现在教室有大桌子

分析：
before 是以前的意思 所以第一句be动词 用are过去式were
now是现在的意思 所以第二句be动词 用are

造句：
第一句：There was a small blackboard in the classroom before. 以前教室有小黑板
第二句：There is a big blackboard in the classroom now.现在教室有大黑板

第一句：There was no computer in the classroom before. 以前教室没有电脑
第二句：There is a computer in the classroom now.现在教室有台电脑。
你看下图片是一台还是很多台，如果有很多台就是：
There are computers in the classroom now. （computer用复数，be动词用are）

第一句：There was no a map of China in the classroom before.以前教室没有中国地图
第二句：There is a map of China in the classroom now.现在教室有中国地图

主要的知识点是：
There was/were...before：以前有...
There was no...before：以前没有...
There is/ are...now： 现在有...