D.
Strings are exactly the same thing as waxing. It last the same amount of time. The only difference is that instead of pulling out all the hair at once (waxing) you pull out a few hairs at a time (string). I had my eyebrows done on the 18th and I've been plucking them the past couple days. I liked the string better for my eyebrows because she had more control over what hair was removed. But all in all I don't think there is any difference.