President Truman gave $13 billion in aid to European countries after World War II primarily as part of the Marshall Plan. The most accurate answer among the options provided is:
d) he wanted to boost the sale of European goods to help those countries recover.
The Marshall Plan aimed to provide economic support to help rebuild European economies, which in turn would lead to increased trade. By aiding in the recovery of these nations, the United States sought to prevent the spread of communism and promote political stability in Europe. While options a) and b) touch on aspects of U.S. foreign policy at the time, option d) most directly aligns with the primary goal of economic recovery and stability in post-war Europe.