I believe the answer is: D. The space race
In the 1950s, United states and the soviet union are involved in a cold war due to the difference in their ideological system.
To prove to the rest of the world which country have the superior technological advancement, both countries involved in a space race to be the first one that place a man outside the planet earth.
To obtain the fund needed for the researches, governments in both countries obtain a loan from another countries and increase the national debt.
