Express as the Logarithm of a Single Expression $\log _ { b } x - \log _ { b } y$

Multiple Choice

Express as the logarithm of a single expression. Assume that variables represent positive numbers.
- $\log _ { b } x - \log _ { b } y$

A) $\log _ { b } x - y$
B) $\log _ { b } \frac { y } { x }$
C) $\log _ { 2 b } \frac { x } { y }$
D) $\log _ { b } \frac { x } { y }$