1 . What is the coefficient of $x^{10}y^{20}$ in the expansion of $(2x - 3y)^{30}$?
(a)
$\binom{30}{10}\cdot 2^{20}\cdot 3^{10}$
(b)
$\binom{30}{20}\cdot 2^{20}\cdot 3^{10}$
(c)
$\binom{30}{20}\cdot 2^{30}\cdot 3^{10}$
(d)
$\binom{30}{20}\cdot 2^{10}\cdot 3^{20}$
(e)
$-\binom{30}{10}\cdot 2^{20}\cdot 3^{10}$