Which of the following is a monomial?
A. 9/x
B. 11x^2
C. 20x - 14
D. 20x^9 – 7x
ITS B: 11x^9

Mono (1) nomial == 1 term.
11x^2 is 1 term in combination so B is your answer.
D. is not, its a binomial along with C. and A.