KE is energy of motion . For air and other gases, it is common to consider the KE to be proportional to the number of molecular collisions.
More collisions means higher temps while less collisions means lower temps.
The three temperature scales must be known for the quiz. Kelvin scale is called the absolute temperature scale because it is the only scale that directly measures energy. There are negative temps on the other two scales and it is impossible to have a negative energy. Gravity causes the air to be concentrated in this layer. By definition that implies a very high temperature so the ELR is positive.