I suspect a few things are going on here.
1. The teacher forgot to include that the University wants 100 responses to the survey. 2. Missing answer C likely contains something like "Randomly select 14 more students to receive the survey"
That makes it an actual statistics question, you'd need to calculate the response rate from the original 120 and then compute the additional solicitations required to meet the response count goal of 100.
Each answer has a failing:
A - student didn't have much to say, answers tainted by student being annoyed and clicking through the survey to stop the spam
B - surveyor didn't like the answer they got, so they drew again. that's straightforward biased sampling
D - might not make for enough data, as you said
E - student body isn't stateless, and may have had time to talk about the survey. "Hey friends, let me know if any of you get asked to do that survey because I want to give them a piece of my mind"
Choosing between them is only possible by making some simplifying assumptions, which requires knowing what you're trying to find out.