D. uncharitable.
The suffix -able, borrowed from Old French and originally from the Latin -ābilis (meaning "worthy of being acted upon"), can have different meanings.
The most common one is "fit/liable to be (done)," as in:
- likeable - fit to be liked
- washable - fit to be washed
- degradable - liable to be degraded.
This, however, does not apply to comfortable. Another meaning of -able, however, is "giving, or inclined to," as in:
- comfortable - giving comfort
- (un)charitable - (not) inclined to charity.