ANSWER
B - Air density is lower, so there is less heat transfer
Step-by-step explanation
We want to identify why temperature decreases with higher altitude.
When radiation is absorbed by the earth's surface, it heats the surroundings and the air through convection and conduction.
However, as we ascend higher into the atmosphere, the amount of solar radiation absorbed by the troposphere's gases decreases significantly.
Due to less heat transfer, air molecules start to move away from each other causing a decrease in air density
Hence, we see that temperature decreases with increasing altitude because there is less heat transfer due to the lower air density.
The answer is option B.