The arrow represents which comes after or which comes before i.e a-->b means that a must come before b or b must come after a
Now jump to the given diagram, as it is clear that
i) 2 and 3 must come after 1
ii) 4 must come after 2 and 3 so obvious comes after 1 also
iii) 5 and 6 must come after 4 so obvious must comes after 1,2 and 3 also.
Now follow this step and check with the given options
Hence option D is not correct as 3 does not comes before 1 (point no. i)
NOTE: (2,3) and (5,6) are at same level, therefore their positions can be interchange as in option (A and B) position of 2 and 3 interchanged.