Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information. A. Thermals capped by clouds have upper limits when the temperature gets low enough to condense water vapor. B. Thermals usually stop rising when they reach a cloud, because thermals are limited in the amount of water vapor they can hold before the vapor condenses. C. Most thermals have clouds at their upper end, because thermals stop rising in places cool enough to condense the thermal's water vapor. D. Thermals usually rise to the same altitude as clouds, because cool air in clouds allows the water vapor to condense.