fix(curriculum): Change comma to full stop in explanation (freeCodeCamp#64721)

Author: Dafterfly

curriculum/challenges/english/blocks/zh-a1-warm-up-greeting-new-colleagues/68ece776dbb09b63b4ab41b4.md

@@ -52,7 +52,7 @@ The first syllable in the audio begins with the initial `zh`, not `z`.
 
 # --explanation--
 
-Wang Hua is saying `zhōng guó rén`, The tones for the three syllables are first tone, second tone, and second tone, respectively.
+Wang Hua is saying `zhōng guó rén`. The tones for the three syllables are first tone, second tone, and second tone, respectively.
 
 Pay attention to the initial of the first syllable. The tongue tip should be curled up to pronounce the `zh` sound.