Somebody recently asked me about how to record a learner's answers to quiz questions being marked server side. here's my response:
Thanks for the question! The verb in this case would be 'answered' as shown in the cookbook here.
You'll notice that some of the interactions in the cookbook make use of the result.response property to store the learner's response. This can (and normally should) be used for any type of question. The format of the value of this property is the same as the format of the items within the correctResponsesPattern array. This is an area of the spec where we've added a lot more clarity for the next version. You can see this version under development here: https://github.com/adlnet/xAPI-Spec/blob/1.0.3/xAPI.md#response-patterns
You may also find it helpful to look at the statements generated by the golf example prototype quiz here.
It's worth noting (in case you're not aware) that xAPI tracking can be done server side. if you're marking the questions sever side fort security reasons, you should do the tracking server side too. Here's some code libraries