During an engine's intake stage, what passages inside the cylinder head of a gasoline powered engine must the incoming air-and-fuel mixture flow through in order to enter the cylinder? a. intake ports b. valve guide c. exhaust manifold d. cylinder bore

The answer is the intake ports/valves.  

Engine valves consist of two types of valves; intake and exhaust valves. An intake valve is placed on a cylinder head of an internal combustion engine. It is built to allow or let in the proper amount of air-fuel mixture to enter inside the cylinder when the complete cycle movement of piston from TDC to BDC and then back to TDC takes place.

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