How to indicate in a text area there are more lines of text hidden?

We are talking about a dialog in a Windows desktop application.

I have text areas that most of the time contain only one line of text, but may occasionally contain several lines. Due to limited space it would be great to display the text areas only one line height and if there's more text then somehow indicate the area should be expanded. (the user can expand the area with a simple resize grabber in the corner)

How to indicate that? I made 3 options:

If the ... buttons are clicked the area would grow to show the full content. But which one tells the user that? Do you have any other idea?

Thanks!