A have higher demands of museums
B are open to more people with different social background
C to lengthen their opening hours
D charge too little for admission
E have been built and open to public
F by lowering the admission fees
To meet the needs of society, more museums______.

A．why office doors were often left open
B．when it was a good time to turn off the computer
C．what questions office workers were bothered with
D．which behaviors could tell whether a person was busy