u poor thing, lymph system is part of killing the pathogen, not preventing the entry. therefore the answer is A. don't worry i got 11 wrong because didn't read option c correctly!!!
personally, after doing the 3 unit course i understand your stress... but as cliche as it sounds don't stress. maths is all about practice and refining your skills, if you don't get something in class clear it up soon, it fundamental that you get the basics.
plus you are doing prelim, prelim...
the best way to know whether you are reaching your estimate, is to go on site with an atar calculator, mainly because the data you have given, i cant really say whether or not you are the right track.
what i did was when i got my marks in my school reports, i used the online calculator to...