填空题 从供选择的答案中选出应填入下面一段英文中 1内的正确答案。
   A light-emitting diode (LED) is a semiconductor (1) that emits visible light when an electric current passes throughit.The light is not particularly (2) , but in most LEDs it is monochromatic, occurring at a single (3) . The output from an LED can range from red (at a wavelength of approximately 700 nanometers) to blue-violet (about 400 nanometers). Some LEDs (4) infrared (IR) energy (830 nanometers or longer); such a device is known as an infrared-emitting diode (IRED).
   An LED or IRED (5) of two elements of processed material called P-type semiconductors and N-type semiconductors. These two elements are (6) in direct contact, forming a region called the P-N junction. In this respect, the LED or IRED (7) most other diode types, but there are important (8) . The LED or IRED has a transparent package, allowing (9) or IR energy to pass through. Also, the LED or IRED has a large PN-junction area whose (10) is tailored to the application.
   供选择的答案：
   1．wavelength    2．shape    3．emit    4．device    5．resembles
   6．bright    7．visible    8．consists    9．differences    10．placed