16. In the binomial expansion of ( $\mathrm { a } - \mathrm { b } ) \mathrm { n } , \mathrm { n } \geq 5$, the sum of the 5 th and 6 th terms is zero. Then a/b equals:
(A) $( n - 5 ) / 6$
(B) $( n - 4 ) / 5$
(C) $5 / ( n - 4 )$
(D) $6 / ( n - 5 )$
16. In the binomial expansion of ( $\mathrm { a } - \mathrm { b } ) \mathrm { n } , \mathrm { n } \geq 5$, the sum of the 5 th and 6 th terms is zero. Then a/b equals:\\
(A) $( n - 5 ) / 6$\\
(B) $( n - 4 ) / 5$\\
(C) $5 / ( n - 4 )$\\
(D) $6 / ( n - 5 )$\\