We need some books.改否定句
We don't need /needn't any books.
It's my birthday today.改疑问句
Is it your birthday today?
The girl in the green shirt is Joe.改疑问句
Is the girl in the green shirt Joe?
Can you guess?改肯定句
I can guess.
Can you see any pens on the table?改肯定句
I can see some pens on the table.