In this question, if we look at the first part it is said that the belief of strikes that can turn people of a country against a dictator is false. That means, the blank in the second part means this situation will always right. So only invariably fit in the second blank.
Answer is C.

folly means foolishness, that turns the previous phrase and the next one opposite. thus the peoples belief is foolishness to go around the dictator.

'Rarely' and 'never' can be eliminated as they are opposite of what is required in the blank. 'sometimes' and 'usually' are too similar to differentiate between them, and so, both can be eliminated. Left with 'invariably' - the correct answer.

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