根据对话内容判断下列各句的正误。
Cathy: Mom, look, there are some birds.
Mom: Which bird do you like?
Cathy: I like the green one. It's more beautiful than the blue one.
Mom: Which bird is stronger?
Cathy: The blue one is stronger.
Mom: I like the blue bird. I think it's younger, too.
Cathy: But the green bird's tail is longer.
Mom: Yes, I think it's about 20 cm long.