"La tortue mange du riz."
Traduction :The turtle eats rice.
"The turtle eats rice" = rice forms part of the diet of this turtle we are talking about. The opposite is "The turtle does not eat rice"
"Turtles eat rice" = turtles as a species include rice in their diet.
"The turtle is eating rice" = the turtle is actually eating rice now
"The turtle is eating some rice" = the turtle is actually eating rice now: "some" does not change the meaning it is often more natural to include "some"
Oui mais seulement pour identifier la tortue. par example "The turtle eating rice belongs to me; the one eating bread belongs to John." Nous regardons quelques tortues , une d'elles est en train de manger du riz et une autre est en train de manger du pain , l'une est la mienne l'autre apartien à John.