How longitudinal waves are formed

According to social exchange theory, altruistic behaviors benefit the individual who performs them. t/f

The material that keeps its new shape after it is stretched is called?

Engineers find a new metal that is stronger than steel but much lighter. this material is also significantly cheaper than what is currently used for most aircraft, available in large quantities, and easy to manufacture. the engineers are excited because this new material will lower the costs of buying and operating airplanes for companies. what is probably the best step for the engineers to make next?