The NFC Technology is a Wireless Technology which works in the range of 10 cm or less.
NFC stands for Near Field Communications.
The name itself indicates that it a communication mode with the near by objects.
The NFC technology is used in Access Cards, Payment Cards and Mobile Devices etc.
Option (a) IM - Instant Messaging is the instant text messaging technology sends and receives messages over the internet. It is used in Social Media where instant messaging is available. So, option (a) is not correct option.
Option (b) text messaging the technology is the technology in which the text messages are sent over the mobile networks ( in case of text messaging in mobile phones ) or over the internet ( emails, blogging etc). So, option (b) is not correct option.
Option (d) DES is not a short range wireless technology. So, option (d) is not correct.
First of all, check your router (the thing that gives you internet). Maybe that's the problem. It that doesn´t work, try going to settings and going to WIFI. Then disconnect the WIFI and connect it again. Sometimes the WIFI gets connected, but doesn't like ¨grab¨ correctly, so it keeps falling. Hope this helped.