Questions

In troposphere and mesosphere, temperature declines with increasing altitude. In stratosphere and thermosphere, temperature increases with increasing altitude.The coldest temperatures in Earth’s atmosphere occur at the top of mesosphere, the Mesopause, especially in the summer near the pole.Transitional layers of atmosphere include tropopause, stratopause, and mesopause. These layers are relatively thin and are located between major layers of atmosphere. These have contrasting thermal properties. Hence, in these layers there is no change in temperature with change in altitude.

The question tag ‘isn’t it’ needs to be replaced with ‘can’t we’. This is because the sentence and the question tag must be in the same tense and the same pronoun is to be used in the question tag. Thus, the correct formation would be, ‘we can go out whenever we choose to, can’t we?’

If some action has started in the past and is still continuing, then present perfect continuous tense should be used instead of present continuous tense. So, the phrase ‘am waiting’ needs to be replaced with ‘have been waiting’ to make the sentence contextually correct. Thus, the correct formation would be, ‘I have been waiting for three –quarters of an hour’.