Why are there few or no clouds in the stratosphere

 Air in the stratosphere is dry and thin
It's the global depression.

In the lower part of the stratosphere, the temperature does not change with height. But, in the upper part , temperature increases with height. At 50km, the temperature is about 7o/c. Air in the stratosphere is dry and thin, and there are very few or no clouds.

The correct answer should be brand c.