Answer:
D. Atomic Bomb
Explanation:
The atom bomb was not present until the late World War II era
It feared that Europe wanted to infringe on the newly gained US independence. They were afraid that European countries that were developed enough wanted to gain control of various portions of the American continent. This would limit the growth potential of the US as a country.
A law about horse-drawn carriages
The index of leading indicators is used to predict changes in business cycles. The correct option among all the options that are given in the question is the first option or option "a". It is basically used to predict the future of the upcoming economy. It can also be said that it does not always yield the perfect result.