In French "it" has no other translation than [cela/ceci] or [ça/c'] (more used). Ex : "Ça fait mal !" / "It hurts !". "C'est trop dur !" / "It's too hard !".
Please note that it's the same translation for "this/that".
In English, animals and babies are designated by "it". It's not the case in French, they all have a gender, so for those, you have to use either "il" or "elle", and certainly not "ça" or "c' ". I'm being specific on this one because it could be considered as very rude to do so.
You might need to do some research on articles and prepositions.
Here is a link to start :
"Ils man gent du riz" shouldn't be accepted.
The two correct sentences are :
- "Il mange du riz"
- "Ils mangent du riz"
And you're right, there is absolutely no difference in pronunciation between those two sentences, that's why both are correct (but only for the oral exercise of course).
When talking about food or drink in french do you say 'some' before the food or drink par example, " Je bois de l'eau," or, "Il mange du riz."