The correct answer is A. solar cells.
Solar cells are the most common type of power source used on satellites. They are made of semiconductor materials that convert sunlight into electricity. Solar cells are very efficient at converting sunlight into electricity, and they do not produce any pollution.
Dry cells are a type of battery that uses a chemical reaction to produce electricity. Dry cells are not as efficient as solar cells, and they produce pollution.
Nickel-cadmium cells are a type of battery that uses nickel and cadmium to produce electricity. Nickel-cadmium cells are more efficient than dry cells, but they still produce pollution.
Lead-acid batteries are a type of battery that uses lead and acid to produce electricity. Lead-acid batteries are the least efficient type of battery, and they produce the most pollution.
In conclusion, solar cells are the best type of power source for satellites because they are efficient, pollution-free, and reliable.