(2) Choose three out of five people, and there is a choice method of C53, that is, there is a choice method of 10, and then 10*A33=60.

(3)Cn2=36, so we can get n=9.

(4) According to the definition, x+x-3= 15, so x=9.

(5) [2n * (2n-1) * (2n-2) * (2n-3)]/(4 * 3 * 2) =120 * n * (n-1)/2, and finally find the value of n.

(6)*** has nine terms, the middle term is the fifth term, the coefficient of the eighth term is one, and the binomial coefficient is the eighth power of X.

(14) select d.