A waste-spark-type ignition system fires how many spark plugs at the same time?

A waste-spark ignition system is designed to improve efficiency and reduce the complexity of the ignition process, particularly in a four-stroke engine. In this system, each ignition coil fires two spark plugs simultaneously. This occurs during the combustion cycle for one cylinder while the other cylinder connected to the same coil is in the exhaust stroke, effectively "wasting" the spark.

This simultaneous firing means that the system can minimize the number of ignition coils required, as each coil serves two cylinders. When one cylinder is ready to ignite its air-fuel mixture, the other cylinder is expelling exhaust gases and does not need a spark. Therefore, the design allows for two plugs to be fired at the same time, optimizing the ignition cycle.

The other options, while they mention individual aspects of spark plug firing (like polarity), do not accurately represent the operational characteristic of the waste-spark ignition system as a whole, since the key operational feature of firing two plugs at once is not included in those descriptions.