Boeing helped the United States during World War II by operating several bases to train troops.

increasing its shipbuilding activities.

expanding its commercial fishing operation.

becoming a key aircraft producer.​

operating several bases to train troops

Correct answer is (d) becoming a key aircraft producer.

Explanation:

In Washington, Boeing proved to be a very important aircraft producer during the war. Washington proved to be an important place for this manufacturing to happen because of the plentiful amount of aluminum, which is necessary for construction of these planes. That was available in Washington.