The correct option is "1 only" because carbon fibers are indeed widely used in the aerospace and automotive industries due to their high strength-to-weight ratio, contributing to fuel efficiency and performance. However, statement 2 is incorrect; while recycling carbon fibers is more complex than other materials, there are emerging technologies and processes that enable the recycling of carbon fiber composites, allowing for reuse in various applications. This emphasizes the importance of sustainable practices in material engineering, which is a relevant concept in current environmental science discussions covered in UPSC preparatory materials.