I think I understood the general idea of fruits vs fruit, but what about the situation where you're saying: "My favorite fruits are grape"?
This made me cringe when I saw it in an English course booklet. Would I be correct to assume that, in this case, we would say: "My favorite fruit is grapes"? The reason being that my favorite fruit is. But also, grapes is considered one group or type of fruit here, therefore fruit = is grapes.
Did I explain this correctly? Is this the right assumption? I think that "favorite fruits are..." would be used if you're going to say "grapes and apples".