Answer:
"The probability that Christina will not choose all action movies can be expressed as 1 − 9^C3/20^C3"
Explanation:
The combination of choosing r things for m total things is given as mCr
In total, there are 9 + 7 + 4 = 20 movies
So choosing 3 movies from action movies will be 9C3
And choosing 3 movies from total number of movies is 20C3
Thus, probability of choosing action movies is:

Also, we know probability of something NOT happening is
1 - probability of that thing happening
Hence, probability that Christina WILL NOT CHOOSE all action movies is:

Correct answer choice is last option.