Read the following article and answer the question. Article: Fed up with constantly having to recharge or replace batteries in your ever-expanding electronic devices? The solution may be just a few steps away. "Energy harvesting" promises to power countless consumer devices, often with nothing more than your body's movement or heat. Dozens of companies around the world already offer such products, but many experts believe the market for the technology could explode due to electronic devices being developed for the Internet of Things. "It's huge," said Graham Martin, CEO of the EnOcean Alliance, a San Ramon-based group of businesses that promotes wireless energy-harvesting technologies. With the Internet of Things expected to combine billions of devices, "if they are all battery-powered, we'll have a problem because there's not enough lithium in the world," he added. "So a lot of them will have to use energy harvesting." Among the most basic forms of the technology is body power. When certain materials are squeezed or stretched, the movement of their atoms creates an electrical charge. Automatic watches have employed the concept for decades, for example, by winding themselves when their user moves their arm. Now, the concept is being considered for a number of other devices. In a contest seeking visionary ideas for wearable technologies, Intel awarded $5,000 for a concept to change the temperature difference between a person's body and a special piece of clothing they'd wear into electricity for mobile devices. Using sound to power devices is another energy-harvesting variation. Stanford University engineers are testing smart microchips that create electricity from ultrasound to power implantable devices that can analyze a person's nervous system or treat their diseases. A textile research association in Spain is proposing to obtain electricity from radio waves that flow around everyone to power sensors sewn into clothes, which can monitor a person's heartbeat or other vital signs. Research firm IDTechEx has estimated that annual global sales of... Question: What makes "energy harvesting" necessary according to the passage? Answer:

Select from:
A). The waste of lithium in the world..
B). The increasing number of electronic devices..
C). The development of technology..
D). The pollution caused by batteries..
The answer is:
B).