Over time, the spoils system developed into a
a. merit-based system.
b. political reform movement.
c. political machine system.
d. civil service movement.

The best and most correct answer among the choices provided by the question is the third choice "political machine system."
In politics and government, a spoils system (also known as a patronage system) is a practice in which a political party, after winning an election, gives government civil service jobs to its supporters, friends and relatives as a reward for working toward victory, and as an incentive to keep working for the party.

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