I think it might be the first one: hiv infections. (hope this helps!)
Answer:
four
Explanation:
Carbon atoms have four electrons in their outer shell. So, it exhibits tetravalency & thus, a single carbon atom can form a maximum of four (4) bonds with other atoms
Air will move from hot area to colder area as the temperature at both lands should be equal.
Answer: because there is no sunlight
Explanation: Solar cells are also called as photovoltaic cells. They convert light energy to electricity