Cutting the Confederacy Off from Sea-Borne Commerce Proved Difficult at First

Cutting the Confederacy off from sea-borne commerce proved difficult at first because

A) British merchant ships aggressively pushed through to Southern ports and challenged the Union's authority to block their trade.
B) Confederates relied on allied coastal tribes to harass the Union navy with small attacks from the shore.
C) the strategy of a naval blockade was new and had never been tried before.
D) the Union only had 42 ships to patrol 3550 miles of Confederate coastline.
E) Southerners did not need foreign imports anyway and happily ignored the Union occupation of New Orleans, for example.