ignore the person
introduce yourself, apologize for not remembering their name but say where you met them before
walk up to him or her and say, "Hi, mate!"
try to find out the person's name from others at the event and then introduce yourself.
答案：introduce yourself, apologize for not remembering their name but say where you met them before（ignore the person：在这种情况下不应该装作没看见）。
5: When expressing thanks to a business client who has given you a gift, you should:
send an e-mail because it is faster and more efficient
send a handwritten note
call within 72 hours
a verbal thank you is enough
答案：send a handwritten note (call within 72 hours：虽然应该72小时之内回复，但仅仅打一个电话是不够的。)