In the question below four words are given in bold. These four words are may not be in their correct position. The sentence is then followed by options with the correct combination of words that should replace each other in order to make the sentence grammatically and contextually correct. Find the correct combination of the words that replace each other.

In his relentless conducting (A) of knowledge, the scientist spent years pursuit (B) understanding (C) research that pushed the boundaries of human groundbreaking (D).

Correct option is C

The interchange needed between the words ‘conducting’ with ‘pursuit’ and ‘understanding’ with ‘groundbreaking’ to make the sentence correct.
Thus the sentence will be,
In his relentless pursuit of knowledge, the scientist spent years conducting groundbreaking research that pushed the boundaries of human understanding .