Can you answer these riddles and explain the wordplay?

Here are the answers to the riddles:

*a) The answer to this riddle is A keyboard (or a piano).

*b) This riddle serves to entertain and challenge critical thinking skills by playing on the multiple meanings of the word "keys."

*c) Another riddle with a similar answer (using wordplay) is: "What has an eye but cannot see?" The answer is A needle.