Roll Over to get text

On my stage, I have a movieclip, in the movieclip (movieclip A), I have a dynamic text box and {another movieclip with buttons in it} (movieclip B).

How do I rollover a button in movieclip B so that the dynamic text box in movieclip A will show a word. For example, I rollover the ‘News’ button and the text box will show the word ‘news’ I have tried _root.(variable name) = “News” but it does not work…