The correct answer is: C. Hydroelectric
Hydroelectric power plants are expected to have the longest life. They are typically designed to last for 50 to 100 years, and some have even been in operation for over 100 years. This is due to the fact that hydroelectric power plants are very simple machines with few moving parts. They also have a very low environmental impact, which makes them a sustainable source of energy.
Steam power plants are also expected to have a long life, but not as long as hydroelectric power plants. Steam power plants are typically designed to last for 30 to 50 years. They are more complex than hydroelectric power plants, and they have a higher environmental impact.
Diesel power plants are the least likely to have a long life. They are typically designed to last for 20 to 30 years. They are the most complex of the three types of power plants, and they have the highest environmental impact.
In conclusion, hydroelectric power plants are expected to have the longest life. They are typically designed to last for 50 to 100 years, and some have even been in operation for over 100 years. This is due to the fact that hydroelectric power plants are very simple machines with few moving parts. They also have a very low environmental impact, which makes them a sustainable source of energy.