Correct Response: B. Vacuum tubes were originally used in televisions and radios to amplify the very weak signal picked up by an antenna and to make it powerful enough to emit sound from a speaker, or to control an image on a screen. In the mid-twentieth century, the much smaller and more durable transistor (B) replaced the vacuum tube. This resulted in much smaller and more portable televisions and radios. Microprocessors (A) came later and were used for logical computing. Electron guns (C) have been used to produce the images on television screens since the very beginning and continued to be used until they were replaced by the newer flat screens. They were not used in radios. Capacitors (D) predate televisions and radios by more than 100 years. They were and continue to be a common component in practically all electronic devices.
