Answer:
This/that is a bird.
These/those are birds.
This/that is a bee.
These/those are bees.
This/that is a duck.
These/those are ducks.
This's/That's a balloon.
Explanation:
For this & that and these & those, it is author's choice on some occasions but not all. Context also plays a big part. For example, if a friend says "this is what I want to tell you" before telling you a story, clearly the word "that" would not work in this sentence ("that" would only work if your friend is saying this phrase after telling you a story).
