I would add that most French vowel sounds are "pure" (single) vowel, not in diphthongs, contrary to English (e.g. long a as in "fade", long i as in "ride", long o as in "flow", "ow" as in "allow").

What about these French-only vowels?: 1. /ø/ as in ceux /sø/ ('those') 2. /œ/ as in sœur /sœʁ/ ('sister')