Definitely B. I can’t remember the last time I wore panties that weren’t… uh… for bedroom entertainment purposes.
20 pairs of underpants is a lot? I must have at least twice that in my closet. My wife keeps on buying me new ones in the vague hope I’ll throw some of my old pairs away.
That aside, if by any chance I find myself without clean drawers I’d much rather go commando. It’s not as if I haven’t done that before (back in my army years I wouldn’t wear anything under my uniform from May to October), and there’s nothing I hate more than getting out of a nice shower and then having to put on a pair of soiled boxers.
Only time I ever wear underwear is in a miniskirt and even then, it’s a thong. I hate underwear!
I remember watching a stand-up comedian explain how he was a bachelor and he only did laundry when he ran out of clean underwear. So he bought 180 pairs of underwear and only did laundry twice a year.
And I was thinking a real bachelor would wear each pair a second day and only do laundry once a year.
Why, hello there! 
I always grab a pair of clean underwear before I get in the shower, so I’d never get out and discover that I didn’t have one. If I was ready to take a shower and discovered that I had no clean underwear, I’d simply hold off on the shower for that day (I’m not one of those “I must take a shower every day or the world will come to an end” types, and I have a desk job so funk isn’t a real issue in one day) and I’d hie myself down to the store where I’d buy a pack or two of new underwear. I’ve got oodles of underwear for just this reason. 
Then I’d try to remember to do laundry before I ran out again and had to go buy more. So far I’ve never had to do that, so I guess I’m okay.
Are you serious? Never never never never wear a pair of unwashed undies. Better far to do without. I feel the same way about socks. Put on dirty ones? Like, touching my skin? Eew! The idea is unthinkable.
But maybe that’s just me.
For the most part I have stopped supervising my sons’ bathtime/bedtime rituals, but the nine-year-old and I had to have a little talk the other day. After washing a week’s worth of his laundary I folded seven shirts, seven pairs of pants, seven pairs of socks - but only 2 pairs of underwear. Every day, son. Every day.
On the other hand, the five-year-old’s hamper contained closer to 14 pairs of underwear. And at least 20 pairs of socks.