help me with bitcoin and blockchain questions!

Which of the following is true of SHA-256 hash function? It has been proven not to have a collision a However secure it is Bitcoin adopts other hash functions No collision has ever been publicly found It has been proven that there is no fast way to find collisions Which of these keys are required for verifying a signature? The secret key The public key Both the secret and the public key None Keys are required only for signing anyone can verify the signature without a key