To open a dialog box each time an error occurs, which of the following is added to prefs.js? | Java Script

A.  user_pref("javascript.classic.error_alerts", true);
B.   user_pref("javascript.classic.error_alerts ", false);
C.  user_pref("javascript.console.open_on_error ", true);
D.  user_pref("javascript.console.open_on_error ", false);

 Ans: A