What is best to say about a runner who is running at a constant velocity? a. their acceleration is positive. b. their acceleration is negative. c. their acceleration is zero. d. their acceleration cannot be determined.

Which of the following is part of the explanation or description of electromagnetic waves? (select all that apply) a. electrically charged molecules in a medium transfer their energy to nearby electrically charged molecules. b. a changing electric field causes a changing magnetic field. c. magnetic molecules in a medium transfer their energy to nearby magnetic molecules. d. a changing magnetic field causes a changing electric field.