What is ischemia? coronary infraction?

What is ischemia?

It can affect your heart, your intestines, and any part of your body. If this happens it can end up triggering a sequence that leads to your death.

Ischemia is..

an inadequate supply of oxygenated blood to all or part of a tissue or organ as a result of an obstructed or constricted blood vessel.

Not sure what you mean by "Coronary infraction?", but

The word "infarction" comes from the Latin "infarcire" meaning "to plug up or cram."

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."