can you tell me why the answer B is right? text questions:Excuse me ,sir. Would you do me a favor? of couse. what is it?I___if you could tell me how to fill out this form? A had wondered B was wondering C would wonder D did wounder Why not choose C?
Hello, Guest Emotion: smile

"I wonder if" and "I was wondering if" are commonly used to "soften" requests.
Instead of saying, for example:
"Excuse me, sir. How do I fill out this form?", which is perhaps too direct and which sounds more like a demand than a request when you address a stranger of whom you're going to ask a favour, you use "I was wondering if" (even more polite that "I wonder if").

"I would wonder" doesn't make much sense in that dialogue. It means something like "I might wonder in the future", which is not the case here. You are already wondering if the man will help you.

I hope it helps.