The correct answer is D. It should be capable of starting quickly.
A peak load plant is a type of power plant that is used to meet the increased demand for electricity during peak hours. Peak hours are typically the hours of the day when people are at home and using more electricity, such as in the morning and evening. Peak load plants need to be able to start quickly in order to meet this increased demand.
Option A is incorrect because peak load plants do not need to run at high speed. In fact, some peak load plants, such as gas turbines, are designed to run at very high speeds. However, this is not an essential requirement for a peak load plant.
Option B is incorrect because peak load plants do not need to produce high voltage. In fact, some peak load plants, such as diesel generators, produce low voltage. However, this is not an essential requirement for a peak load plant.
Option C is incorrect because peak load plants do not need to be small in size. In fact, some peak load plants, such as combined-cycle power plants, are very large. However, this is not an essential requirement for a peak load plant.
Therefore, the correct answer is D. It should be capable of starting quickly.