Which reason do you believe is most significant to the US entry into the way and why?

Explanation:

The entry of the United States was the turning point of the war, because it made the eventual defeat of Germany possible. It had been foreseen in 1916 that if the United States went to war, the Allies' military effort against Germany would be upheld by U.S. supplies and by enormous extensions of credit.

i believe it d) heterogeneous

porter is writing economic history because he is focusing on the cost of developing vaccines.