When ordering a new airplane, airines must choose the style of three major components, each of which has about ten variations. This is an example of A. modular design. B. robust design. C. CAD. D. environmentally friendly design.

The scenario described involves airlines selecting from various styles of three major components, each with multiple variations. This is indicative of a design approach that allows for flexibility and customization in the manufacturing process. The correct answer is: **A. modular design.** ### Explanation: - **Modular design** refers to a design approach that divides a system into smaller parts (modules) that can be independently created and then used in different systems. In this case, the three major components with multiple variations represent a modular approach, allowing airlines to customize their airplanes according to their specific needs. - **Robust design** focuses on improving the performance of a product under varying conditions, which is not the primary focus here. - **CAD (Computer-Aided Design)** is a technology used for design and technical documentation, but it does not specifically relate to the concept of choosing variations in components. - **Environmentally friendly design** pertains to designs that minimize environmental impact, which is not mentioned in the context of component selection. Thus, the best fit for the scenario is modular design.