Which statement best defines the least common denominator (LCD) for rational expressions?

Given denominators $12x^2$ and $18x^3$, which of the following is the least common denominator?

Compute the LCD for the denominators $9x$, $20x^2$, and $14$.

Factor $x^2+x-20$ completely over the integers.

Add the rational expressions: $\frac{2}{x+3}+\frac{x}{x^2+6x+9}$