Take One example which satisfy given constraint in question.
A= {40,50,60}
B={10,20,30}
Both Array have n elements and they are in non-decreasing order(they may contain equal no.s in asc. order)
C={10,20,30,40,50,60}
Array index starts with 0.
Now take i=2
A[2] >= B[2]
So now check all options
I. C[4] >= A[2]. 50 >= 60 . False
II.C[4] >= B[2]. 50>= 30 . True
III.C[4] <= A[2]. 50<=60. True
IV. C[4] <= B[2]. 50 <=30. False
So Option C is Correct Ans.