What is the likely outcome if spark plugs that require immediate attention are not replaced?

When spark plugs that require immediate attention are not replaced, the outcome can encompass a range of negative effects on vehicle performance, which explains why all of the listed options are interconnected consequences.

Reduced fuel efficiency occurs because worn or faulty spark plugs can lead to incomplete combustion of the air-fuel mixture, causing the engine to work harder to maintain power, thus using more fuel than necessary.

Engine misfiring is a direct result of malfunctioning spark plugs. If a spark plug isn't igniting the fuel-air mixture properly, it causes the engine to run inconsistently, which can lead to rough idling or stalling.

Poor acceleration can also be attributed to bad spark plugs. When the ignition system isn't firing correctly, the power output of the engine is compromised, leading to sluggishness during acceleration as the vehicle struggles to maintain speed.

Therefore, the correct answer acknowledges that neglecting to replace spark plugs that require immediate attention can lead to all these adverse effects on vehicle operation.