Answer: A. from subjunctive to indicative
Explanation: An inappropriate shift or inconsistency in the verb of a sentence confuses the reader. Shifts in a verb mood can make reading difficult and obscure the sentence's meaning. In this sentence, the mood of the verb changes from subjunctive to indicative. To correct the shift, both clauses in the sentence should be in the same (subjunctive) mood: If you were to sit more comfortably, is you would not fall off.