A little bird told me the answer is (D).

Yes, the answer is D.
And I did as you guys told, by splitting the whole network into 2 halves, and thereafter solved it using series-parallel, but as I reached the bottom row I ended up with an unbalanced Wheatstone bridge as you said. But I don't know what to do after that.

 

That's exactly the approach I took. And of the two delta choices you have, one of them is balanced. You can solve it for the exact solution without using a calculator in just a few minutes.

Yes, thanks! I was considering the unbalanced Delta form, that is why I was unable to solve it (tedious maths!) . After considering the balanced Delta form, I got the answer!

 

Yes, thanks! I was considering the unbalanced Delta form, that is why I was unable to solve it (tedious maths!) . After considering the balanced Delta form, I got the answer!

Great!

Often times you will face multiple paths to an answer. All should get you there, but not with equal effort. So it is good to develop the habit of pondering what the various options are and trying to evaluate which one is best. And don't be afraid to acknowledge that you got tricked and made a bad choice -- just go back and pick another route. Sometimes the one that looks the most intimidating actually turns out to be the easiest.