Answer:
They require more testing in real-world conditions.
Step-by-step explanation:
They produce more noise pollution than other cars. - this answer is incorrect. There have not been any records of the high noise pollution of the hydrogen fuel cell car. There is no reason why they would produce more noise.
They have had unpredictable electrical problems. - this is not a correct answer. The hydrogen fuel cars don‘t have electrical problems. The only potential problem can be that hydrogen is a flammable element, but this does not have anything to do with the electrical components of the car.
They have not yet been driven over long distances. - this is not true. There have been tests and people driving these cars.
They require more testing in real-world conditions. - This is the correct answer. The production of cars that run on hydrogen fuel is expensive, and there is not high demand yet, therefore it has not been tested in real-world conditions much. While there are people using these cars, there are no worldwide conditions for their usage, which is why it is not profitable to start mass production of these cars and make them available to the public so far, and test them that way.