The correct answer is B. GPS. In artificial intelligence history, GPS stands for General Problem Solver. It was an early AI program developed to simulate human problem-solving behavior. GPS was designed to solve problems by breaking them down into goals, subgoals, operators, and differences between the current state and the desired state. This approach became important because it introduced structured reasoning and symbolic problem solving, which were central ideas in early AI research.

LPS, MLS, AIS, and EPS are not the standard answer for the first useful computer program in the AI world in this context. GPS is widely recognized as one of the earliest useful AI programs because it attempted to model general reasoning rather than solving only one narrow calculation task. It showed how computers could be programmed to search through possible actions and work toward a goal. Therefore, the correct answer is B. GPS.