Answer: B

First, substitute to make y/xz simpler. Since y = x^3 and z = x^4:
y/xz = (x^3) / (x)(x^4)
= x^3 / x^5
= x^3 / (x^2)(x^3)
= 1/x^2

We're looking for the square root. Take the square root of both the numerator and denominator, which leaves 1/x, choice (B).