What is the relationship between paragraphs 1 and 2?
正确答案：D
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Structural Mechanics
Structural mechanics refers to how structures behave under various forces. Engineers use principles from this field to design buildings, bridges, and other items to ensure they can withstand loads and stresses. For example, when designing a suspension bridge, engineers need to know the weight of vehicles that cross it (live load) and the bridge's own weight (dead load). They must also calculate how earthquakes and high winds may affect the bridge. Recently developed "smart" materials change their properties in response to external stimuli, such as temperature, light, or electrical fields. Shape-memory alloys (SMA) can "remember" their original shape. After being deformed at a lower temperature, some SMAs can return to their original shape upon heating. Applications for this technology include orthodontic wires and stents for medical purposes and wing flaps and jet engine components in aerospace. Experts in structural mechanics use computer simulations to identify potential weaknesses and optimize designs for safety and performance. Nevertheless, predicting the long-term behavior of structures under real-world conditions remains a challenge. Environmentally sustainable design is also taking on greater importance. Engineers increasingly use eco-friendly materials and design structures to minimize energy consumption.
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