Please answer the following question by reasoning step-by-step.
He was ready to bike home, he got out his key and began to what?\nOptions:\n- turn lock\n- pocket\n- solution to problem\n- pocket\n- open doors

turn lock
Turn lock is to fasten something, usually with a key.

He was ready to bike home, he got out his key and began to turn lock.

.

So, the answer is turn lock