To display more than one line of text for a text question, navigate to the question's configuration by selecting the cogwheel icon on the right-hand side of the question. Then toggle on "Allow multiple lines of text" and set the number of lines desired under "How many lines of text should the question be?".
Gotchas
This won't stop people from entering more or fewer lines of text. It will only change the default size of the text box that is displayed.