How did roosevelt assist britain while maintaining u.s. neutrality?

C.  Stimulated manufacturing in New England.

Explanation:

President Thomas Jefferson in 1807 passed Embargo Act, which lasted between the period of December 1807 to March 1809, with the purpose of harming the United Kingdom and France during the Napoleonic Wars.

During this period, all areas of the United States suffered economic downturn.

In commercial New England and the Middle Atlantic states, ships could not work and were staying idle at the wharves, and in the agricultural areas, notably in the South, it prevents the farmers from selling their crops on the international market.

However, this scarcity, stimulated and spurred New England, and especially for the Middle Atlantic states, to the development of American both in manufacturing and agricultural industry.