What is term? please help me​

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

Waves are used in many practical applications to support work, entertainment, and health. one example is the use of ultrasound imaging to safely track the development of a growing fetus. what is a specific example of a practical application of waves in medicine, entertainment, safety, or other fields? provide a brief explanation of how the properties of waves are useful to that application.

It is really hard for me right know