His friend insisted that he must, but his conscience stopped him as he knew that he what?\nOptions:\n- unnecessary\n- optional\n- will not\n- need not\n- should not
Let’s work this out in a step by step way to be sure we have the right answer.
should not
Should is not is used when one wants to stop.

Should not is used in contrary to must.

.

The final answer: should not