An engine is described as having an efi fuel system. the abbreviation efi indicates that the engine uses a
a. type of fuel-injection system.
b. supercharger.
c. turbocharger.
d. carburetor.

a. type of fuel-injection system.

Explanation:

An engine described as having an efi fuel system uses an electronic fuel injection system. It is a form of fuel-injection system that is developed to improve on the limitations of its fizzled-out counterpart - carburetor.

EFI systems have various components making it better than the carburetor.

Some of which are;

Engine control unit, fuel tank and injector, throttle sensor and a fuel delivery system.