In a 30-60-90 triangle there is a rule that shortest side of triangle (the one oposite from 30 degrees angle) is 2 times shorter than hypothenuse. so lets search for that match in offered answers.
A. shortest side is 4√3 and hypothenuse is 8√3 which doesnt match condition. B. 4 and 8 is just what we need. That is correct answer. but now we need to check third side. It has to be √3 times shortest side. it indeed matches C. 4 and 8, atches first condition but other side isn't √3 times shortest D. 4 and 8√2 doesnt match first condition