A. nCr(3r-2n)

B. nCr(3n-r-2n-r)

C. nCr(3r+2n-r)

D. none

^{n}C_{0}+^{n}C_{1}+^{n}C_{2}+………+^{n}C_{n} =

If the 5^{th} term is 24 times the 3^{rd} term in the expansion of (1+x)^{11} then x=

If T_{r+1} is the term independent of x in (3x-5/x^{3})^{8} then r=

The 4^{th} term of (1-2x)^{-1} when x=1/3 is

If x^{r} occurs in the expansion (x+1/x^{2})^{2n}, then its coefficient is: