Score by answer not an option for multiple response?

The trick is pretty simple. 

In the base layer - Create a blank slide and include your question text (in a text box). Next, add the answer options. For each answer option, provide a check box or a radio button. Declare a variable with a name and its default value set as 0. Enable triggers for each check box. For each correct answer that the user selects, add a trigger that increments the appropriate marks to the variable. For incorrect answers, increment the variable by 0.

Next, add a button (on the base layer) to reveal three layers - correct, partially correct, and incorrect. In the 'correct' layer, add suitable text for all correct answers. Include the following (without the double quotes) - "Your score is %variable name declared by you%". This configuration enables SL to reveal you total score. 

Add suitable text and reveal the score for partially correct and incorrect layers. Finally, add triggers for the button on the base layer to show the suitable layers with conditioning. (If variable = 0, if variable = 1 etc.). 

If you would like to use the default 'Submit' button, you need to enable the same and configure suitable triggers. In this case, the 'Submit' button requires a validation of the variable and we need to 'show' the corresponding layer.

Hope this helps!