Can you solve this riddle for a STEEM prize?

If you have three, you have three.
If you have two, you have two.
But if you have one, you have none.

What am I?

Source

There is a grand prize of 0.005 STEEM for the winner and three 0.001 STEEM runner up prizes.

The winner is the first correct answer. After 7 days the runners up will be randomly selected. I will use a random number generator and assign numbers to all correct answers and the three chosen will win (It's a small prize but mainly just for fun). After 7 days I post an answer/identify the correct answer and pay out the rewards.

Please optionally upvote if you like this post or give an answer, have fun!