What type of power is normally used to operate the pushbutton switches for closing the passenger door?

The use of the left battery to operate the pushbutton switches for closing the passenger door is correct due to the standard power distribution system in aircraft. The left battery is typically one of the primary sources of electrical power in many aircraft systems, including those controlling door operations.

Switches such as those for closing passenger doors require a reliable and readily available source of power, which the left battery provides during normal operating conditions. The other sources of power, such as the internal generator, right battery, or external power unit, may serve as additional power sources in specific scenarios but are not designated for routine door operation.

In most cases, using the left battery ensures that the system functions efficiently and reliably, as this part of the electrical system is designed to handle essential functions critical to passenger safety and convenience.