What Was Henry Clay's "American System

What was Henry Clay's "American System"?

A) A package of protective tariffs to promote manufacturing and federal expenditures for internal improvements
B) A program that revised the steps by which aliens might become naturalized U.S.citizens
C) A system of trade agreements with European nations stipulating that imports and exports must be made available in equal amounts
D) A bill in Congress stipulating that only native-born Americans could occupy important government posts