Certain questions can have more than one answer. Sometimes, there are an infinite number of correct answers; as soon as an answer corresponds to certain conditions, it is deemed to be correct. For example, any numeric value in the range of 600 to 1000 can be the right answer. Equations can have more than one root. Answers can be right or wrong if certain conditions are met. There are literally limitless possibilities of making creative questions and still getting the benefit of fully automated grading!
Example 1: simple condition