用括号里的疑问词提问

用括号里的疑问词提问
Various products are on display at the fair.(what,where)
We send many letters and postcards every day.(who,what)
Wang Ping keeps his books in a cabinet.(who,what,where)
Our Export Fair takes place in Guangzhou twice a year.(what,where,how often)
There are four samples on the desk.(how many,what)