Final answer:
The correct form of the verb to complete the sentence is 'met', making the full sentence 'When I first met him, he was studying'.
Step-by-step explanation:
The sentence provided, 'When I first _________( meet) him, he was studying', is in the past tense; hence, the correct form of the verb to use would be 'met'. This is because 'meet' is an irregular verb in the English language, and its past simple form is 'met'. Therefore, the correctly completed sentence should read, 'When I first met him, he was studying'.
Learn more about Past Tense