Under Chinese National Standard GB 5768 (Road Traffic Signs and Markings), what does a yellow equilateral triangular sign with a black border depicting an arrow curving sharply to the right (向右急弯路) signify?

1. Mandatory right turn lane ahead
2. Prohibition against turning right at the upcoming junction
3. Warning of a sharp right-hand curve ahead requiring reduced speed
4. Expressway right-hand exit ramp guide