'Project Loon', sometimes seen in the news, is related to

1. A

   Waste management technology

   Waste management. Project Loon is not a landfill or waste-to-energy project. This letter is not the key.

2. B

   Wireless communication technology

   Wireless communication. Alphabet/Google’s Project Loon used high-altitude balloons to beam internet connectivity to the ground—a wireless last-mile idea. That stored letter is the official key.

3. C

   Solar power production technology

   Solar power production. Balloons may carry solar panels for their own power, but the project’s purpose is connectivity, not utility-scale solar. This letter is not the key.

4. D

   Water conservation technology

   Water conservation. Loon is unrelated to watersheds or irrigation. This letter is not the key.

Summary. Official key is (b) wireless communication technology. Project Loon floated stratospheric balloons to deliver internet. It is not waste, solar-farm or water tech. Honour the stored letter (b).