Clause 8.4 (subclause "a")

Warning signs inform drivers about approaching a dangerous section of the road and the nature of the danger, indicating that measures must be taken to ensure safe passage through this section.

Clause 33.1 — 33 "Road signs", 1 "Warning signs", sign 1.1 "Dangerous right turn"

Warns about a road curve with a radius of less than 500 m outside populated areas and less than 150 m within populated areas, or about a curve with limited visibility. The sign is installed outside populated areas at a distance of 150–300 m, and within populated areas at a distance of 50–100 m before the start of the dangerous section. If necessary, the sign may be installed at another distance, which is indicated on plate 7.1.1 "Distance to the object".

Clause 33.1 — 33 "Road signs", 1 "Warning signs", sign 1.4.1 "Direction of the turn"

Indicates the direction of the road turn marked by sign 1.1 "Dangerous right turn", the direction for bypassing an obstacle on the road, and, in addition, the direction for bypassing the center of a roundabout. On curves with a radius of less than 1000 m outside populated areas and less than 250 m within populated areas, it is permitted to use a sign that represents part of sign 1.4.1 (a single arrow). In this case, it must be repeated along the curve at a distance from 3 m to 85 m, depending on the radius of the curve.

(Application for this question: sign 1.4.1 is not a sign for advance warning about approaching — it is used to indicate/accompany the turn itself (direction) on the dangerous section.)

Clause 33.7 — 33 "Road signs", 7 "Plates to road signs", plate 7.8 "Direction of the main road"

Indicates the direction of the main road at an intersection. Used with signs 2.1, 2.2, 2.3. The plate is placed directly under the signs with which it is used.

(Additionally, for option elimination: does not relate to warning about a dangerous turn.)

Clause 33.5 — 33 "Road signs", 5 "Informational and guiding signs", sign 5.18 "Lane direction"

Indicates the permitted direction of movement in a lane. A sign with an arrow depicting a left turn in a manner other than provided by these Rules means that at this intersection a left turn or U-turn is made by exiting to the right beyond the intersection and bypassing a traffic island (divider) in the direction indicated by the arrow. A sign that allows a left turn from the far left lane also allows a U-turn from this lane. The effect of a sign installed before an intersection applies to the entire intersection unless the next sign 5.16 or 5.18 installed at the intersection gives other instructions.

(Additionally, for option elimination: this is not a warning sign about a dangerous section of the road.)

Thus, the correct answer is "Sign 3.", considering that according to the definition in the Traffic Rules, it is the warning sign 1.1 "Dangerous right turn" that warns in advance about approaching a dangerous section (dangerous turn) and is installed before the start of the dangerous section.

The key word in the question is "approaching." According to the Traffic Rules (subparagraph "a" of point 8.4), it is specifically warning signs that inform the driver in advance that there is a dangerous section ahead and indicate the nature of the danger so that the driver has time to prepare for safe passage.

Among the proposed options, only sign 1.1 from section 33 (warning signs) directly means "Dangerous right turn." It is used when the curve has a small radius or limited visibility, that is, there is a risk of not making the turn at the usual speed. Importantly, this sign is placed in advance: in populated areas 50–100 m before the turn, outside populated areas 150–300 m (or at another distance if specifically indicated by a supplementary plate).

For comparison, the "Direction of turn" sign (1.4.1) is mainly used directly at the turn itself to indicate the direction to follow, not to warn about approaching a danger. The "Main road direction" supplementary plate concerns priority at intersections, and the "Lane direction" sign regulates permitted directions in a lane, so they do not warn about a dangerous turn.

Therefore, the correct answer is "Sign 3," since it is warning sign 1.1, which informs in advance about approaching a dangerous right turn and gives the driver time to reduce speed and prepare for safe passage.