I'm stuck with bottom corner
17a Animals produce it, humans leave it (6) ??t?e?
17d 50 is 10? Pay attention! (6) ??s?i?
20d For centuries they ignored America (4) m?ds (mods)??
13d Don't leave out! (8) r?k?n?l? (only word I can come up with is rekindle) ??