General Rochambeau helped General Washington by providing French troops for the Battle of Yorktown.
attacking General Gates at the Battle of Camden.
attacking General Greene at the Battle of Guilford Court House.
providing British ships for the Battle of Camden.

Correct answer is providing French troops for the Battle of Yorktown.

Explanation:

First option is correct as Rochambeau is correct, because he participated in the most important battle of the war, where he was one of the most important factors that led to surrender of British army.

Second option and thus the fourth option is not correct as battle of Camden is battle between Great Britain and United States, where troops were led by Cornwallis and general Gates.

Third option is not correct as it was another battle where French troops did not participate. Cornwallis fought there against general Greene.

d. migration of french settlers into english colonies

the anwser is a) to prevent military conflict