What setting of the reverser may cause the inability to drive a single-carriage tram?

In the drawing we see three settings of the reverser in a single-coach tram. The tram may be unable to move if the reverser is set to "0" - the answer is A.

The reverser is the switch for the direction of travel: position "P" means driving forwards, "T" means driving backwards, and "0" is the neutral position, in which the tram does not move. When the reverser is at "0", the tram will not move off, even if you press the drive pedal. The "P" setting (answer B) allows you to drive forwards, and "T" (answer C) backwards. When the tram does not move off, after checking the doors you check the position of the reverser.

Legal basis: Art. 3 para. 1 of the Road Traffic Act (Prawo o ruchu drogowym)