Questions 17-20 are based on the following passage. You now have 15 seconds to read ques-tions 17-20. 17. Why does the speaker say that radiation is similar to radio waves? [A] Because both of them can be detected by human senses. [B] Because both of them can be sensed by a radio receiver. [C] Because both of them are harmful. [D] Because both of them can only be detected by devices.