To add additional parts to a TeX  question, simply add more designations (ex: %%%%%%%%%%%% quest 2 , %%%%%%%%%%%% expl 2) to the body of the question:

/* This is a comment describing the question
%%%%%%%%%%%% quest 1
Here is the text for my first question part. TeX equations, multiple choice options, images, and lists can go here. 
%%%%%%%%%%%% expl 1
Here is the explanation for the first question. 
%%%%%%%%%%%% quest 2
This is the second question part. 
%%%%%%%%%%%% expl 2
And its corresponding explanation. 


As well as additional answer variables to the code portion:

/* global double ans1 u={}*/
/* global double ans2 u={}*/


ans1 = 1;
ans2 = 1;


For more information about the code portion of TeX Open questions, please visit this page.