Which of the following uses is not acceptable for flexible cords?

Flexible cords are designed for specific applications, and their use is regulated for safety and functionality. The option stating that flexible cords can be "attached to building surfaces" is indeed not acceptable. This practice can pose safety hazards, as flexible cords are intended for flexibility, movement, and temporary connections rather than being secured to a surface. If a cord is fastened to a building surface, it may become subject to physical damage or stress that can lead to a malfunction or create a tripping hazard. Therefore, using flexible cords in ways that prevent their intended movement and flexibility is not compliant with electrical codes and standards.

In contrast, using flexible cords for temporary wiring, connecting portable devices, or for lighting fixtures is generally acceptable, as these applications align with the design and purpose of flexible cords. They allow for mobility and temporary setups, making them suitable for temporary installations and equipment that require occasional repositioning.