If I --try--, I will pass the test.
If I study, I'll pass the test.

This will be the answer if we don't have to insert more than one word.

Answer Justification:
There can also be other words used e.g. concentrate et cetera as we have to insert something that's suitable and appropriate, meaning which is making sense in the meaning of the sentence, but for the sake of different types of minds of people who check your answers, insert the words that you think the person who checks your answer will find correct.
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