About Lighting and reflection of the trailer: which statement is correct?

A trailer only needs a fog light if it was put into service after 31 December 1997.
If the trailer's reflectors are clean, you are visible enough even without the trailer lights on.
✓ Extra marker lights are required if the trailer is longer than 6 metres and/or wider than 2,10 metres.
The white retroreflectors of a trailer belong at the rear.

Correct answer: Extra marker lights are required if the trailer is longer than 6 metres and/or wider than 2,10 metres.

Explanation

Extra marker lights are required if the trailer is longer than 6 metres and/or wider than 2,10 metres.

This trailer itself must always have a rear fog light. The only exception is if the TOWING vehicle itself has no fog light. The law does contain a date nuance for older heavy trailers, but the exam follows the book: treat the rear fog light as always mandatory.
Reflectors are an addition; the trailer must also have rear lights, brake lights and indicators that work together with the car's lighting.
White retroreflectors belong at the FRONT; at the rear are red triangular reflectors. Red rear, white front.