Question

I’m very upset with my cousin! I told him I wanted to surprise my mom with a new painting, and he told her my plan. I wish I’d known he can’t keep a secret because then I wouldn’t have told him mine!

A.
writing on the wall

B.
let the cat out of the bag

C.
grab the bull by the horns

D.
green with envy

Answer 1

You don't actually ask a question here but the answer that would make sense here would be b.
He let the cat out of the bag (Aka shared the secret)

Answer 2

I think your answer is B, Hope this helps