Which words in this sentence are an independent clause?

An American businessperson discovered a stockpile of King Tut's items that had been hidden in a safe tomb, which had a clay sealing covering it.

A.
which had a clay sealing covering it

B.
An American business person discovered a stockpile of King Tut's items

C.
that had been hidden in a safe tomb

D.
that had been hidden in a safe tomb, which had a clay sealing