Question

david bushnell was a student at yale college in the early 1770s when he invented the american turtle submarine. it was a small submarine powered and manned by only one person. the pilot pedaled to propel the submarine forward and controlled the rudder by hand. to control the depth of the vessel, the pilot had to adjust the amount of water within the vessel. he would let water in to submerge it and use a hand pump to get the water back out so he could float again. it was the first submarine used during combat.
at the time, the american turtle submarine was

unnecessary

vulnerable

massive

advanced

Explanation:

To solve this, we analyze the description of the American turtle submarine. It was the first submarine used in combat, had a unique propulsion and depth - control system (pedaling for forward movement, adjusting water for depth). "Unnecessary" is incorrect as it was used in combat, so it had a purpose. "Vulnerable" is not supported by the text as there's no info about it being easily harmed. "Massive" is wrong because it's described as "small". "Advanced" fits because it was an innovative design (first combat submarine with its unique operation methods) for its time.

Answer:

D. advanced