How can a driver distinguish between a Maximum Speed Limit sign and a Minimum Speed Limit sign under GB 5768?

1. Maximum speed limit is a white circle with a red border and black numbers; Minimum speed limit is a blue circle with white numbers and a bottom white arc
2. Maximum speed limit is yellow; Minimum speed limit is green
3. Maximum speed limit is triangular; Minimum speed limit is circular
4. Maximum speed limit is blue; Minimum speed limit is red