Question

what was one main reason khrushchev was replaced as party leader?
his reforms created serious problems.
he was unable to win the space race.
his challenge to the us nearly caused a war.
he was forced to crush rebellions in other countries.

Explanation:

Khrushchev's reforms, such as agricultural and industrial ones, had issues like the "Virgin Lands Campaign" which didn't yield expected results and created problems. The space race wasn't a direct leadership - removal reason. The Cuban Missile Crisis (challenge to US) was a tense moment but not the main reason for his removal. Crushing rebellions (like in Hungary) was part of the Cold - War era but not the main cause of his replacement. His reform - related problems were more fundamental in losing support.

Answer:

His reforms created serious problems.