The correct answer is B) opens as soon as the load current exceeds its setpoint. The key characteristic of an "instantaneous-trip" single-element type fuse is that it opens the circuit as soon as the load current exceeds its predetermined setpoint, without any intentional time delay. This rapid response is achieved through a simple, heat-sensitive element that melts and interrupts the circuit once the current reaches the fuse's rated value. In contrast, the other answer choices describe different fuse types or characteristics that are not associated with an instantaneous-trip fuse. For example, time-delay fuses (option C) introduce a preset delay before opening, and self-resetting fuses (option D) are a different category of protective devices.