I would like to know whether my brother's answer is right.
The question is to find two errors and correct them based on the dialog.
G: Hi, I'm looking for a T-shirt. Which T-shirt do you recommend?
M: I recommend this green one. It's our most popular model.
G: Do you have it in another size?
M: Yes. We have four sizes. Would you prefer a smaller or a bigger one?
G: I'd prefer a smaller one.
M: Then what about this T-shirt? It's the smallest of the four sizes, and it's on sale now.
G: That's just what I need. I'll take it.
M: Ok. Do you need anything else?
G: No, thank you. That's all.
-> I bought this green T-shirt today. It's a popular model, and it comes in four different colors. I chose one that is not on sale. I think I made a perfect choice.
So, my brother corrected (colors -> sizes) and (is not -> was). But his teacher said that the second one was incorrect because my brother should have changed "is not" just into "is".
If "is not" is changed into "was", is it incorrect? Rather I thought that answer is more accurate.