Paper is ________ useful invention.It was invented around 2，000 years ago by Cai Lun.（　　）

A．aB．anC．/D．the

﹣﹣﹣Shall we go out and do some outdoor activities？

﹣﹣﹣_______.（　　）

A．You're welcome

B．That's a good idea

C．Don't worry

D．It's none of your business

﹣﹣﹣Our class won the first prize in today's basketball match.

﹣﹣﹣_______ exciting news it is!We're all glad about it.（　　）

A．WhatB．What anC．HowD．How an

﹣﹣﹣You _______ take photos here!Look at the sign.It says"No photos".

﹣﹣﹣ Sorry，I won't.（　　）

A．mustB．needC．mustn'tD．needn't

﹣﹣﹣I am going to sell all your old books.They are taking up a lot of space.

﹣﹣﹣______ !They're everything to me.If you sell them，you will take my life.（　　）

A．I couldn't agree more

B．You can't be serious

C．It's nothing

D．Sounds good