We do not offer the "Poll question" option. So if you embed a multiple choice question and you select more than one answer as correct, the students will have to select all the right answers in order to get full credit. We suggest you create an open ended question, maybe offering some answer ideas, so your students can give you some feedback without having bad grades.
If you have some troubles grading your students or you're afraid it can be difficult, please follow this article to learn how easy it can be!
Here is a video that might be useful.