Important history questions having trouble with.

A few questions I need to make sure are correct.

According to historian Alfred Thayer Mahan, the key to a great nation's power was it's-
(A) army
(B) navy
(C) frontier
(D) democratic government.

The Seventeenth Amendment provided for the direct popular election of-
(A) U.S. senators
(B) U.S Representatives
(C) the President
(D) state governors

The "Open Door" policy was a United States' effort to keep trade what country to all open nations-
(A) Japan
(B) Lithuania
(C) China
(D) all of these

What system has a free enterprise economy with farms and factories privately owned-
(A) capitalism
(B) Communism
(C) socialism
(D) none of these

in which branch of the United Nations does every member nation have an equal vote-
(A) General Assembly
(B) Security Council
(C) Secretariat
(D) Trusteeship Council