I don't know the context, but I think this is about explaining which kind of animal. So A is the correct one. This is because we use "the" to show that something is specific and to talk about something general. We do not use it to talk about plurals that are not specific. For Example, if I say, "She likes cats," I am saying that she generally likes cats, and it doesn't matter which kind or whose cats. But if I say, "She likes the cats," I am saying that she likes a specific group of cats, maybe my friend's cats, or the cats that she saw at the pet store. I hope this helps.

This is one of those questions where context is everything. None of them are wrong. A is the answer to the question "Are those dogs or cats?" C is the answer to the question "Are those the dogs that I'm supposed to take to the veterinarian?" (or another question that is asking about a specific group of dogs or cats) B&D can also be used in some situations, but would be a little more rare.

A. They are cats, not dogs. Makes sense. Best option in my opinion. B. They are cats, not the dogs. Does not make sense to omit "the cats" but then use "the dogs" C. They are the cats, not the dogs. Makes sense and depends on context whether you'd use this or A. D. They are the cats, not dogs. Like B, it sounds awkward and doesn't really sound natural. We are (the) humans, not (the) animals. We are (the) friends, not (the) enemies. The "the" is not necessary in these instances. If there was a group for example or a species called "friends" then it would make sense to say "we are the friends" however generally speaking you would just say "we are friends"

Ugly grammar explanation: sentences using "to be" (copulaic) with an indefinite plural do not get an article (a / an / the). That's a boring way of saying this: Yes: "We are humans" -- No: "We are the humans." Yes: "You are men." -- No: "You are the men." Yes: "They are cats, not dogs." -- No: "They are the cats, not the dogs." Yes: "We are friends, not enemies." -- No: "We are the friends, not the enemies." --- ** It may be a bit easier to understand when you look at the singular forms: I am /a/ human. --> We are humans. You are /a/ man. --> You are men. It is /a/ cat, not /a/ dog. --> They are cats, not dogs. I am /a/ friend, not /an/ enemy. -> We are friends, not enemies. In other words: I am /a/ human. --> We are // humans. -- where // represents the "zero article" or the empty space where an article should go. --- The second sentences (after "No: ...") are not wrong, but they are not indefinite. "You are /the/ men" assumes that we have been talking about some men previously. You almost always have some explanation after it -- introduced by "that" or "which" -- for example: "You are the men that helped me!" A famous line from Star Wars: "These are not /the/ droids that you are looking for." "the droids that you are looking for" is specific idea.

I'll go for letter A. In this case, no article is necessary for each noun.