Answer:
Third Option:
“I just had my car keys, but now I can’t find them anywhere. Has anyone seen my keys?”
Step-by-step explanation:
First, the comma separates the now from the keys statement. This allows the sentence to flow more smoothly.
Second, the ”Has anyone seen my keys?” Is a question — in which it needs to be sepearated from a statement; “...but now I can’t find them anywhere.”