You can now add a "score" to an answer within the multiple choice question. The extra field can be found after the "Limit Action" column:
A numerical "score" can be allocated to an answer and upon selecting that answer it is recorded against a recipient's response. If multiple score answers are selected across the survey they are added together and displayed within the final response. If no scores are added to questions/answers it will default as 0.
If you are looking to create a quiz style survey assign the correct answer to a question a score of "1" and leave the other answers (incorrect) blank or 0. When the responses are exported the final score will be how many questions they got correct.
For more information about surveys please click here.