The one thing it is impossible for God to do

Today I have three riddles for you:

1. What is the one thing it is impossible for God to do?
2. What is the one thing God forgets?
3. What is the one man-made thing in heaven?

I kid you not, all three riddles have a biblical answer. (#1 and #3 are found in the New Testament; #2, in the Old Testament.)

Offer your solutions in the comments, and I’ll let you know whether you were right!