7. What did the British blockade of the North Sea contribute to?

It prohibited all American trade with the central powers.

Explanation:

it contributed highly to the outcome of WW1

americans had many intangible advantages. well since the british fought a war far from home military orders, troops, and supplies sometimes took months to reach their destinations, and the british had an extremely difficult objective. they had to persuade the americans to give up their claims of independence, americans had a grand cause: fighting for their rights, their independence and their liberty. this cause is much more just than waging a war to deny independence.

i think the answer is b.