Is the word 'what' singular or plural? I asked my teacher and he says you can use it both ways.<br/><br/>a) What has happned is unfortunate.<br/><br/>b) What have happened are unfortunate.<br/><br/>c) Here are what I know.<br/><br/>d) Here's what I know.<br/><br/>I think that only a) and c) are correct. What are your opinions?