Simple answer - Give points for a correct answer
How does it work?
If the answer is correct, the student gets the number of points indicated in the marking rule. If the answer is incorrect, the student gets zero points. How strict the marking is, depends on the added accepted answers and the question settings.
How to add the marking rules?
It is possible to name your marking rule and choose how many points a correct answer is worth:
This is what it looks like when a marking rule has been added to a question: