Final answer:
The correct answer is 'jovial,' as it describes a cheerful and friendly manner which would suit a stand-up comedian.
Step-by-step explanation:
For the sentence 'Gary's _____ manner often led people to say he should become a stand-up comedian,' the correct word to fill in the blank is 'jovial'. 'Jovial' means cheerful and friendly, qualities that would likely lead others to suggest Gary has the personality for a stand-up comedian. The other options, 'dour' which means relentlessly severe, 'melancholic' which suggests a deep sadness, and 'pensive' which implies a thoughtful or reflective state, do not align with characteristics typically associated with comedians.