What is the meaning of the word 'obtuse' when described through contrast?

The term "obtuse" generally refers to someone who is not quick to understand or lacks sharpness in intelligence. This is particularly highlighted when contrasted with words that imply intelligence or sharpness. In this context, the opposite of being smart or quick-witted would be being unintelligent, which aligns perfectly with the choice indicating that "obtuse" signifies a lack of understanding or awareness.

When looking at the remaining options, "smart" and "talented" are definitions that run counter to the concept of being obtuse, as they imply sharpness and capability in understanding or skills. The option "complex" does not directly relate to intelligence. Therefore, the answer that best encapsulates the meaning of "obtuse" through contrast is the one that describes someone lacking in these qualities, which is unintelligent.