Answer:
in a region with a letter
Explanation:
For a certainty, then probability is 1.
That means sum of probability of all events in the sample space.
This means P(A)+P(B)+P(C)+P(D)=1
This is equivalent to:
P(A or B or C or D)=1
Hence for certainty, the region must be:
A or B or C or D
So the correct answer is in a region with a letter.