Step-by-step Solution:

Logical Deduction

The best way to solve this is to build a simple map of the parallel roads' relative positions based on the given clues.

1. 
   Establish Key Positions:
   
   
   
   • We are given a direct link: K is 1/2 km South of J. This means the distance between J and K is exactly 1/2 km.
   
   
   • We can build on this: K is 1 km North of G.
   
   
   • And also: I is 1 km North of J.
   
   
   
   


2. 
   Evaluate the Options based on these positions:
   
   
   
   • A. I and K: The distance from K up to J is 0.5 km, and from J up to I is another 1 km. Total distance = 1.5 km.
   
   
   • B. J and G: The distance from G up to K is 1 km, and from K up to J is another 0.5 km. Total distance = 1.5 km.
   
   
   • C. I and G: The total distance is G → K (1 km) + K → J (0.5 km) + J → I (1 km) = 2.5 km.
   
   
   • D. J and K: The distance is directly established as 1/2 km.
   
   
   
   

Final Arrangement

This logic results in the following map (from North to South):

   (North)
      ^
      |
      I
      |
    1 km
      |
      J
      |
   0.5 km
      |
      K
      |
    1 km
      |
      G
      |
      v
   (South)

Conclusion: The calculations and the visual map confirm that the pair of roads 1/2 km apart is J and K.

Final Answer: The correct option is D.