During strenuous exercise, tv plateaus at about 60% of vc but minute ventilation continues to increase. explain how that would occur.

The elevation in the residual volume, which takes place leads to a corresponding reduction in the expiratory reserve volume and inspiratory reserve volume. Though at rest, the total volume is large enough to offer enough concentration of oxygen required by the tissues and to eradicate the carbon dioxide produced by the tissues.  

The enhanced strenuous exercise like climbing a flight of stairs needs more oxygen and produces more carbon dioxide. However, as resting inspiratory reserve volume and expiratory reserve volume have diminished, the total volume cannot enhance much to meet the gas exchange requirement of the body and the person becomes short of breath.  

"do a testcross with a homozygous recessive plant."

option c is the correct answer.