Why are clouds so flat from the bottom and so fluffy at the top?

Because air pressure decreases at the rate of 0.91 inches per 1,000 feet of ascent, rising air expands and cools. The flat bottom of cumulus clouds defines the exact height at which a critical combination of temperature and air pressure causes water vapor within the rising current to condense into a visible cloud

you didn't give any options but heres what i can tell you: an inference is likely to change based on additional observations. the latter is something that you have seen or sensed using your sensory organs while the former is like a conclusion out from what you have observed.