An exterior raceway containing service entrance conductors must be ______ and arranged to drain.

The correct choice is that an exterior raceway containing service entrance conductors must be tight and arranged to drain. A tight raceway is essential for protecting the conductors from environmental elements such as water and moisture that can cause short circuits, corrosion, and other electrical hazards. The design ensures that these conductors are safely contained and that no gaps exist where contaminants could enter.

Additionally, having a drainage arrangement is crucial because it allows any water that does accumulate inside the raceway to escape, thereby minimizing moisture retention. This aspect is particularly important for service entrance conductors, where reliability and safety are paramount due to their critical role in providing electrical power to a building.

The other options do not provide the necessary protective features required for safety and compliance with the electrical codes. Loose or flexible raceways might not adequately safeguard the conductors from water ingress, while a secure arrangement does not address the requirement for drainage. Therefore, a tight configuration is necessary to meet safety standards and ensure the longevity of the electrical installation.