In recent weeks, the speculators have been waging on all-out war on the american dollar. the strength of a nation's currency is based on the strength of that nation's economy - and the american economy is by far the strongest in the world. accordingly, i have directed the secretary of the treasury to take the action necessary to defend the dollar against the speculators.

i have directed secretary conally to suspend temporarily the convertibility of the dollar into gold or other reserve assets, except in amounts and conditions determined to be in the interest of monetary stability and in the best interests of the united states.

-richard nixon, august 15, 1971

which of the following statements describes a major cause of the policy shift outlined in the passage?

a. the u. s dollar's value had fallen steeply each year since the conclusion of world war ii.
b. several european leaders had agreed to establish the bretton woods system.
c. the american gold mining industry had collapsed as a result of its monopolistic structure.
d. foreign countries had begun exchanging their u. s dollars for gold at an increasing rate.