句型转换。
Dave and his friends are doing their homework now.(改为否定句)
Dave and his friends ________ their homework now.
He is reading a book now.(改为一般疑问句)
_______ he ________ a book now?
The boy in blackis playing chess.(对画线部分提问)
_________ playing chess?
My grandparents are having supper now.(对画线部分提问)
________ your grandparents ________ now?
Ben is playing the guitar inthemusicroom．(对画线部分提问)
________ Ben _________ the guitar?