How HIV Affects and Its Treatment using Combination Therapy
a) HIV uses a certain receptor that's expressed widely on T helper cells. As this is homework I suggest looking at the wikipedia article to look this up for yourself. It is under tropism. 

b) You mentioned mutation. That's very true but this question is excluding people with that mutation called the delta 32 mutation. Thus HIV can infect these people, but what happens to any virus in the context of infection? How does the human body deal with viral infections. Is there any variation that would account for why some people can be resistant to HIV and others not be? 

c) Yes! Well done :) You're thinking along the right lines. Look up the drug on wikipedia and look up it's mechanism. 

d) i) Yeah exactly that. But more than that. There's optimal HIV which in the absence of drugs does the best job at infecting. If we give a drug then HIV has to mutate away from optimal HIV to stay alive, but it's weaker. Give multiple drugs and it can't mutate away from all of them because if it did it would be so far from optimal it would be a rubbish virus. 

ii) 1) It could affect the HIV binding receptor protein or the protein with which it binds on the host cell. So both! Logic would dictate we would use self receptor blockade because at least they're more conserved but I'm sure both are probably used. Enzymes and receptors are both proteins. 

2 + 3) Look up the lifecycle of HIV

e) Theoretically possible. He might not take the drugs. If he takes the drugs unlikely because the virus basically becomes undetectable. Look this up, it should be on wikipedia again.