Final Answer:
The command called repetitively over and over again as long as the Arduino has power is 1) loop().
Step-by-step explanation:
In Arduino programming, the loop() function is a crucial part of the code structure. The loop() function contains a series of programming statements that are executed repeatedly in a loop as long as the Arduino is powered on. It is where the main program logic, often involving tasks such as reading sensors, controlling outputs, and making decisions, is placed.
The setup() function, on the other hand, is executed only once when the Arduino starts. It is used for initializing variables, setting pin modes, and other one-time setup tasks. Options 2 and 4, (output) and (input), are not valid commands in Arduino programming.
Option 1 (loop()) is the answer.