I believe the answer is D.
slow down due to increase of triglycerides in the blood.
All of the cells found in the blood come from bone marrow. They begin their life as stem cells, and they mature into three main types of cells— RBCs, WBCs, and platelets.
I am not sure because there may be more context, but here is what I am guessing the answer is.
As Bryson pedaled uphill both his heartbeat and breathing rate increased. His breathing rate increases to provide the body (more specifically, exercising muscles) with oxygen at a higher rate and his heart rate increases to deliver the oxygen (and glucose) to the respiring muscles more efficiently.
If a person requires greater return when risk increases, that person is said to be:
risk averse
