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First Create the survey
Create Page Break's at the desired points. For example, if you have a survey with 10 questions and would like the first five questions to be taken by the first respondent -- create a Page Break after question 5.
Next make sure that Enable Save And Continue option is checked under the
page. This will allow the first user to save his response.
Make sure you give instructions to the respondents to click on Save and Continue after finishing their part of the survey.
Their response will be saved. They can then enter the email address of the next person that needs to finish of the survey.
Upon entering the email address of the next respondent, an email will be sent out with the URL to continue on with the survey.
The next respondent can then click on the link and finish off the survey.