One oder ones?

Wähle „one“ oder „ones“ für die markierten Satzteile aus.
Just look at those T-Shirts!

1 Which T-Shirts? Which ?
2 The T-Shirts in that shop window over there. Which ?
3 Oh yes. They're nice. I like the red T-Shirt. Which ?
4 I do, too. But I think the blue T-Shirt is nice, too. Which ?
5 Let´s go inside. I'll try the red T-Shirt. Which ?