How to display add'l rows based on dropdown

Hi,

I am trying to create a template with a series of questions with responses of Yes or No. A Yes answer would require further information. If the answer is No, there are no further information required. The additional information is not defined (will vary and contain text/paragraphs), therefore I need to allot a number of rows.

I have created a drop down list for Yes or No already but what I don't know is how to trigger the insert/display of the additional rows if the answer is Yes.

What is the best way to do this? Thanks a lot in advance.