Once you have added the answers to the multiple choice questions, click on add "Other" link (highlighted in the image below). Your users will be able to choose one of the existing answer choices or type their own short answer.
You can use the Go to section based on answer option for multiple choice question so that users only see certain sections based on their answers.
Click Submit to finish.
To use this feature, you need our Gsuite addon. Install this addon to customize Google Forms.
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