When parking along the roadside, park at a _________ angle to the curb.

When parking along the roadside, parking at a 90-degree angle to the curb is correct because this position allows vehicles to fit neatly in parking spaces designated for perpendicular parking. This angle helps to maximize the number of vehicles that can be parked in that area while ensuring that the parked vehicle remains safely out of the traffic lane, thus minimizing the risk of accidents.

Parking at a 90-degree angle also facilitates easier entry and exit from the parking space, as drivers have a clear view of oncoming traffic when leaving the curb. This position aligns with common parking regulations that prioritize safety and effective use of space.

Other angles like 45 degrees, slight, or parallel may not offer the same level of safety or efficiency in terms of space usage and visibility when maneuvering in and out of parked positions. These angles are often associated with specific parking designs or may require additional maneuvering space that isn't always available on busy roads.