What if your brother wakes up at the crack of what lawn dawn yawn fawn flaw or crawl?

Think about it. Do any of these make sense?

My brother wakes up at the crack of lawn.

My brother wakes up at the crack of dawn.

My brother wakes up at the crack of yawn.

My brother wakes up at the crack of fawn.

My brother wakes up at the crack of flaw.

My brother wakes up at the crack of crawl.

The only one that makes sense is dawn!