2.5.3.1. Video: How to Pronounce the R Sound in English - YouTube - https://www.youtube.com/watch?v=5hC6bRLr1PU

2.5.3.2. Video: R Sound | Learn English Pronunciation - YouTube - https://www.youtube.com/watch?v=3k7jN4kX4U

2.5.3.3. Article: Minimal Pair /r/ and /l/ | Learn English - https://www.englishclub.com/pronunciation/minimal-pairs-r-l.php

2.5.3.4. Article: English Pronunciation: The R Sound - Hadar Shemesh - https://hadarshemesh.com/magazine/r-sound/