5 The early morning air was cool and _____. A hot B warm C mild

Explanation: The sentence describes the early morning air. 'Cool' suggests a low temperature. 'Mild' is a good descriptor for air that is not too cold and not too hot, fitting well with 'cool'. 'Hot' is the opposite of cool. 'Warm' is also possible but 'mild' often encompasses a pleasant, moderate temperature.

Answer: C mild