This patient with a history chronic hypertension is most likely suffering from left heart failure (decreased cardiac outpout), causing the blood to back up in the lungs (Crackles are heard bilaterally, shortness of breath) and that resulting into increased afterload for the right side of the heart, raising the pressure in the right heart chambers, which get transmitted back to central vein.
High cardiac output to the pulmonary circulation during exercise will cause the distension and recruitment of micovessels and that would cause the increase in total cross-sectional area.
Here are two images that illustrate this principle nicely:
When a muscle runs out of fuel (eg, glucose) and/or producing less ATP and “increased” accumulation of metabolites (all other options besides the correct choice), it is a sign of onset of muscle fatigue. The stem is asking which of the following will “decrease?”, and it is the pH that will decrease (acidosis) due to the accumulation of lactic acid (remember glycolysis pathway where pyruvate gets converted to lactic acid).