Does it matter if you have three or four possible answers when making a multiple choice test for learning? I have built several apps in Norwegian about hunting, philosophy etc. Students use the app to learn a subject and test their knowledge before doing their exam. In current state i have one question with three alternatives, where one is correct. The student will be presented with the solution to the question after they have chosen the alternative, and not on the end of the test. 

For example:

What is the the capital city of Australia?


Canberra
Sydney
Melbourne


I was wondering if anyone know if there is any research on if students learn more/less/equal by being presented with 4 alternatives instead of three. 

For example:

What is the the capital city of Australia?


Canberra
Sydney
Melbourne
Edmunton


Does this have any effect for learning, since it's less probable to just check the correct by chance. Maybe students have to do more active thinking since it's more alternatives to think about, and therefore learn more?
The standard for multiple choice questions is normally 4 answers. However, there is research that indicates that three choices is optimal. Three choices seems to increase the reliability of the test and decreases the number of poor distractors. 

If you are worried about the difficult of your assessment. Instead of developing questions with four choices another strategy would be to increase the number of questions with three choices. This will allow you to cover more content.