What did england do to threaten u. s. neutrality?

a. they stopped many boats going to mainland europe and confused much of the group

b. they used their u-boats to harass u. s. ships

c. they blew up thousands of boats in the north atlantic

d. they invaded charleston harbor

The answer is: c. they blew up thousands of boats in the north Atlantic
The Germany response to this by blowing up several boats that belong to the ally outside the war zone.
Since technically United States held the status as the leader of the alliance, we have no other choice other than to respond and protect the alliance