Since this question is a contrasting sentence with two different subjects, you would use while. "If" implies that it will be a question, and "as" and "when" don't make sense because the sentence conjoins two different contrasting clauses. I hope this helps!

Of course I have tried,but I'm still confused and want to know more so that I come here to ask.I think the answer is D but there are some other views.But still thanks for your advice.

If this is your homework, you should try it yourself first. Look at each option and think about their meanings when paired with the rest of the sentence. If you are still confused, despite confirming the meaning, then come back and rephrase your question in a way that doesn't imply that someone should just give you the answer, as that will not help you learn.