Which of the following refers to passenger cars in the M-series?

The answer refers to MU (Multiple Unit) passenger cars that belong to the M-3, M-7, or M-8 series, which are known for their advanced technological features and modern designs. These specific series of passenger cars are utilized in commuter rail services and represent significant improvements in comfort, safety, and reliability over older models.

The M-3 series marked a transition toward more contemporary design and efficiency, while the M-7 and M-8 series incorporated further innovations, making them well-suited for high frequency and urban transit operations. The systems in these cars are designed to enable multiple units to operate together, increasing flexibility and capacity on busy routes.

In contrast, other options do not apply to the broader context of the M-series passenger cars. While the M-1 series could be an option, it is not representative of the latest developments as the M-3, M-7, and M-8 series are. Single light engines and specialized inspection cars serve different operational purposes and do not fall under the classification of passenger cars within the M-series context.