For which of the following prostheses would biocompatibility not be a serious issue?
A. A hearing aid
B. Contact lenses
C. An engineered arm connected to nerve endings so that it can
respond to brain signals
D. A heart valve

a hearing aid.

it doesn't get in contact with fluids (like contact lenses) and doesn't get implanted, so it got not much to do with the immune system

a rain shadow is a dry region of land on the side that is protected against the prevailing winds of a mountain range. the prevailing winds are the winds that occur most of the time in a particular place of the earth

prevailing winds carry air toward the mountain range. as the air rises up over a mountain range, the air cools, water vapor condenses, and clouds form. on this side of the mountains, called the windward side, precipitation falls in the form of  rain  or snow. this dry air produces a  rain shadow.

the product of the pressure and volume is also constant