下列各句中，没有语病的一句是（)

He is no longer a child，and let him learn to________the problem himself.[ ]

He ________ have completed his work; otherwise, he wouldn’t be enjoying himself by the seaside.[ ]

As a businessman, David is so busy that rarely ______ time for this family.

owed me a red silk dress _____ online,which cost her only 10 dollars.