grammar : what vs. which
“What” is broader than “which”. “Which” … usually means “Which one”. “What” more often means “What kind of”.Here are some examples:
“Which newspapers do you read?” “I read the Houston Chronicle and the Wall Street Journal.” (But not the New York Times, The Guardian, etc.)
“What newspapers do you read?” “Newspapers about business and the stock market.” (= what kind of newspapers)
“Which girl would you like to date?” “The one in the red dress.” (But not one of the other girls in the room.)
“What girl would you like to date?” “One who is intelligent and sweet and pretty.”
Source: usingenglish.com

Me on Google+
Me on Quora