Which best describes the purpose of a controlled experiment? to make sure the results of the experiment support the hypothesis
to prevent a dangerous condition resulting from a reaction
to examine whether one variable causes a change in another
to prevent an undesired change in a variable

Sally turns on her cellular telephone to speak to her friend who is located thousands of miles away. which of the following best describes how such a telephone is able to transmit and receive information? a. the cellular telephone transmits, receives, and encodes information using only sound waves. b. the cellular telephone transmits, receives, and encodes information using only electromagnetic waves. c. the cellular telephone transmits information by electromagnetic waves to a receiver which then encodes them and produces sound. d. the cellular telephone transmits information by sound waves to a receiver which then encodes them and produces electromagnetic waves.