The correct answer is D. progress.
The word “headway” means “progress or advancement, especially in a difficult or complex situation.” In the sentence, “In spite of their efforts, the team of scientists could not make much headway to solve the problem,” the word “headway” is used to describe the lack of progress that the scientists made in solving the problem.
The other options are incorrect because they do not accurately describe the meaning of the word “headway.” Option A, “results,” refers to the outcome or conclusion of something. Option B, “start,” refers to the beginning of something. Option C, “efforts,” refers to the actions that someone takes to achieve something.
In conclusion, the correct answer to the question “In spite of their efforts, the team of scientists could not make much headway to solve the problem” is D. progress.