On one dive to the Titanic, Ballard used a mechanical arm to /

Debris Trails

With just 12 days left over in his mission, Ballard began searching for the Titanic, using this information to track down the ocean liner. He speculated that the ship had broken in half and left a debris trail as it sank. "That's what saved our butts," Ballard said.

Explanation:

disease was the number one killer of native peoples. they had had little exposure to the diseases of europe. this led to some villages being almost completely wiped out and some tribes destroyed.

letter a is the answer