Hi Veronica,
I'll try to answer as best as I can.
d) It relates schedule network activity, assuming we reduce activity X duration by 50% . What are the activities will have crashing points ? What does crashing points refers to ?
I have never heard of "crashing points" before.
e) Does NPV has more risk then EPV ?
As I said, it's irrelevant for the PMP exam. Forget about it.
f) A project manager is working for cost centre manager who also holding another profile - VP operations and oversee projects across 10 countries. PM also has to work closely with the Human resource manager. What kind of project organization ? Functional or matrix ?
From your description this sounds more like a matrix organization to me. Contact the person who originally created this question and ask.
Last question, you are given vouchers of $300 during a conference by the vendor. Should you accept ? The vendor mentioned every participant will get these vouchers too .
Because everybody receives the same vouchers at the conference I see no problem. I would accept it, but I would also disclose it to my superiors.