Greetings! Your answer is "D".
Yes, even if they remain intact, they can still accumulate bacteria and germs.
For most older cars equipped with traditional ignitions, it is recommended to perform a tune-up every 10,000 to 12,000 miles or at least once each year. In contrast, modern vehicles that have electronic ignition and fuel injection systems can typically go anywhere from 25,000 miles to as much as 100,000 miles before requiring a significant tune-up.