21．What extra benefit will you get if you become a member of AAAS right now?

A．$50 as a reward． B．50 issues of Science．

C．A limited-edition T-shirt． D．Unlimited access to online articles．

22．Which membership type charges the most for digital delivery?

A．Regular． B．Post Doc． C．Retired． D．Science Advocate．

23．What's the purpose of the text?

A．To introduce a magazine． B．To invite people to join AAAS．

C．To advertise a website． D．To show AAAS member benefits．

US actor Brent Hill studied the violin for seven years during his childhood．But，now，he couldn't make a sound out of it．His latest role as Dewey Finn in Andrew