4.2.3.1. Video: The Schwa Sound in English - YouTube - https://www.youtube.com/watch?v=3k7jN4kX4U

4.2.3.2. Video: How to Pronounce the Schwa Sound - YouTube - https://www.youtube.com/watch?v=0z1gT2g3w5s

4.2.3.3. Article: The Schwa Sound in English - Pronunciation Studio - https://pronunciationstudio.com/schwa-sound/

4.2.3.4. Article: Understanding the Schwa Sound - Hadar Shemesh - https://hadarshemesh.com/magazine/schwa-sound/