A quick way to pin down "charade" is to think of the common English phrases it appears in today, rather than its older history as a word game.
People often say things like "stop this charade" or "keep up the charade," and in both, the word clearly points to a false show being put on, an act everyone can see through but that continues anyway. That everyday sense lines up directly with "pretense," an act of pretending that is not genuine.
Checking this against the other options confirms the fit. A "series" would need the phrase to be about repetition or order, which "stop this charade" is not about. A "charter" is a formal legal document, which has no place in a sentence about someone "keeping up" an act. A "spate" describes a burst of something happening frequently, again not the sense of a false show being maintained.
Matching "charade" to the phrases it naturally appears in points to one clear meaning among the four options.
So, the correct answer is pretense.
"Charade" is a French word that has kept the same spelling in English, and checking how it's used in modern French confirms its meaning here.
Since the French phrase this word comes from is used for putting on an obvious act, the same sense carried into English, "pretense" is the meaning that fits, not series, charter, or spate.
So, the correct answer is pretense.