Help the bewildered scientist complete his incident report by choosing the correct modal verb.

When the experiment started glowing neon pink and vibrating violently, Dr. Aris panicked. He called his supervisor immediately and asked what he ______ do with the radioactive beaker.

The correct answer is should.

When reporting a question where "shall" is used to ask for advice or instructions (Direct speech: "What shall I do?"), the modal verb backshifts to should in indirect speech. It does not change to "would," which is reserved for reporting "will" or "shall" when they are used for future predictions.