Why did the Allied Navies have such a hard time
stopping the U-Boats?
A
They had never battled submarines before and
did not know how to sink them.
B
The U-boats travelled together in large groups
so that even when one was destroyed many
were left.
They did not have powerful enough guns and
missiles to damage a U-boat.
The U-boats were faster than any other ships
and could spend hours beneath the surface

A

Explanation:

they had never battled submarines before and did not k ow how to sink them

good question. i'll be looking into that. (this is a joke sir)

d. i assume the underlined word is "role." reformat if it isn't.

explanation:

role is closest to part because when replacing words, "playing a vital decision," "playing a vital activity," and "playing a vital dollar" don't make logical sense. the only meaningful choice is "playing a vital part."

this fits one of merriam-webster's definitions of role: "a function or part performed especially in a particular operation or process."