Question

mexico experienced political instability after the revolution because leaders
imposed a new property tax.
were frequently assassinated.
assassinated their enemies.
broke up large estates.

Explanation:

After the Mexican Revolution, political instability was marked by frequent assassinations of leaders. This created a volatile political environment. Imposing a new property - tax, breaking up large estates, or assassinating enemies were not the main reasons for the overall political instability compared to the constant threat and occurrence of leader - assassinations.

Answer:

were frequently assassinated.