The correct choice is (b) SoftwareSerial Library
Easiest explanation: The UART (Universal Asynchronous Receiver Transmitter) is a piece of hardware that allows digital communications between 2 IC’s. The pins on the Arduino that support this are 0 and 1. This functionality is parallel in nature, i.e. the Atmega chip on the Arduino can receive UART data and continue to work on whatever it was working on, at the same time.