1.肯定句形式：主语+was/were +doing (现在分词)+其他。
I was doing my lessons then.
We were cleaning the house at this time yesterday.
I wasn't doing my lessons then.
We weren't cleaning the house at this time yesterday.
否定回答：No, 主语+ wasn't/weren't.
—Were you doing your lessons then?
—Yes，I was. /No,I wasn't.
Were they cleaning the house at this time yesterday?
—Yes, they were./No, they weren,t.
—What was he doing at this time yesterday?
—He was reading books.