Officers of the Foreign Service shall perform the following-enumerated services for American citizens and business organizations in connection with the conduct of foreign trade subject to such rules and limitations thereon as may be prescribed by the Secretary of State:

(a) Answering trade inquiries.

(b) Lending direct assistance to American citizens and business firms.

(c) Encouraging the establishment of, and supporting, American chambers of commerce.

(d) Preparing themselves for and, upon instructions, performing trade conference work when in the United States on leave, or otherwise.