Can someone please explain solving this following Greg’s process to tackle 2 blank TCs?

Is it C,D ?

It is correct. After checking the answer, I was able to trace it via Greg’s method.

For this particular question, you can literally fill anything you think might fit in the first blank and work out the second blank. You’ll get they both must be opposites. Jump to the options and find the opposites (at least that’s what I did). There’s only one such pair.