Given a scientific question, generate a correct answer to it.
--------
Question: What tool do scientist's use to show the evolutionary pathways and connections among organisms?

Answer: phylogenetic tree

Question: Any sound with a frequency above the highest audible frequency is defined as what, a phenomenon useful in medical diagnosis and therapy?

Answer: ultrasound

Question: What type of waves start when a source of energy causes a disturbance in the medium?

Answer:
mechanical waves