1 .
What is the coefficient of $x^{20}y^{80}$ in the expansion of $(5x - 3y)^{100}$?
(a)
$-{100 \choose 80} 5^{20}3^{80}$
(b)
${100 \choose 80} 5^{20}3^{80}$
(c)
${100 \choose 80} 5^{80}3^{20}$
(d)
${80 \choose 100} 5^{20}3^{80}$