2.2.1.1. Video: How to Pronounce TH in English | θ vs ð Sounds - YouTube - https://www.youtube.com/watch?v=5hC6bRLr1PU

2.2.1.2. Video: The TH Sound in English - New and IMPROVED Lesson - YouTube - https://www.youtube.com/watch?v=CYWV4ISaBNM

2.2.1.3. Article: Minimal Pair /ð/ and /d/ | Learn English - https://www.englishclub.com/pronunciation/minimal-pairs-th-d.php

2.2.1.4. Article: How to Pronounce the TH Sound in English - Pronunciation Studio - https://pronunciationstudio.com/th-sound/