Sales assistant: Hi, can I help you?

Customer: Yes, do you have this shirt in blue?

Sales assistant: Yes, here you are.

Customer: Do you have it in a medium size?

Sales assistant: Yes, here you are.

Customer: Can I try it on?

Sales assistant: Yes, the changing room's over there...

(Later...)

Sales assistant: Is it OK?

Customer: Yes, how much is it?

Sales assistant: It's 20 dollars.

these jeans/this dress              black/white

them in a small size/it in an extra large size

them/it

Are they/Is it

are they/is it

They're/It's