Clause 28.3 (Section 28 "Movement of vehicles in mountainous areas")

On mountain roads, it is prohibited to: a) drive with the engine off and the clutch or gear disengaged; b) tow using a flexible coupling; c) any towing during icy conditions.

This clause directly establishes a special prohibition specifically for mountain road conditions: among the towing methods, towing with a flexible coupling (rope) is separately prohibited, regardless of other conditions (and during icy conditions, any towing is prohibited at all).

Therefore, the correct answer is "Towing with a flexible coupling," given that according to the definition in the Traffic Rules in clause 28.3 (subclause "b"), such a towing method is directly prohibited on mountain roads.

When driving on mountain roads, safety requirements become stricter due to steep ascents and descents, curves, and increased loads on the brakes. Therefore, some actions that may be permissible on flat roads are prohibited in the mountains.

Clause 28.3 (b) of the Traffic Rules of Ukraine explicitly states that it is not allowed to tow a vehicle with a flexible coupling, that is, with a rope or cable, on mountain roads. The reason is that during a descent, the towed vehicle, under the influence of gravity and inertia, may start to "catch up" with the towing vehicle, causing sharp jerks on the rope or even a collision with the rear of the towing vehicle if the distance decreases too quickly.

This situation is especially dangerous in curves: due to the change in direction and the effect of centrifugal force, the towed vehicle may deviate from the trajectory of the towing vehicle, the rope loses stable tension, and the controllability of the combination worsens. In such conditions, the risk of swaying, skidding, and loss of control over both vehicles increases.

That is why the rules in the mountains allow safer options, such as rigid coupling or partial loading, but flexible coupling on mountain roads is prohibited.

Therefore, the correct answer is "Towing with a flexible coupling," since on mountain roads a rope does not provide a stable and safe distance and controllability during descents and turns, which is directly prohibited by clause 28.3 (b) of the Traffic Rules of Ukraine.