Engines that operate with rotors instead of pistons or cylinders are seldom used in modern automobiles because a. they don't produce enough power. b. they produce dangerous emissions and aren't fuel efficient. c. they can be highly explosive. d. the batteries are heavy and expensive.

B is the correct option.

Explanation:

There are various factors which makes a rotary engine inefficient for use in automobiles. Some of them include Lubrication, Efficiency and cooling, Emissions and fragility. The emissions of rotary engine are in form of excessive carbon dioxide and hydrocarbons. It is one of main hindrance of its widespread acceptance. The engines are also fragile and can't tolerate oiling, cooling and fuel system failures like piston engines do. It also has more than average fuel consumption since the combustion chamber is long and the ares in contact of the combustion mixture leads to loss of energy.

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