Questions 14 to 16 are based on the following passage. At the end of the passage, you will be given 15 seconds to answer the questions. Now, listen to the passage. Which one is NOT true about the waterbeds
A．They can be heated by electric mat or infrared lamps. B．They are made from tough plastic membrane. C．They are the best choice in the scientific test. D．They are much safer for the piglets but hard to control.