Use Comment Box for long answer questions.
How to configure a question using Comment Box:
Go to Toolbox portlet on the left side of the screen in the survey builder.
Click on Comment Box. The question type is populated on the section page.
Click on the question, Configuration portlet displays on the right.
Click on the Required check box if you want to make this question mandatory for the surveyee to complete.
Click Save when you are done with the configuration.