Question

the first investigators determined the uss maine sank because of an outside mine. a mechanical error. spies on the ship. a bomb onboard the ship.

Explanation:

The sinking of the USS Maine was a significant event. Initial investigations pointed to an external cause. An outside mine was the conclusion of the first investigators. This was a key factor in the lead - up to the Spanish - American War as it was used as a rallying cry (remember the Maine).

Answer:

an outside mine.