Institution: জাতীয় কবি কাজী নজরুল ইসলাম বিশ্ববিদ্যালয় (JKKNIU) Exam: ক ইউনিট || জাতীয় কবি কাজী নজরুল ইসলাম বিশ্ববিদ্যালয় || 2013
Topic: Sentence (বাক্য), Subject: English Grammar (ইংরেজি গ্রামার)

Best Answer Explained in Below-:

The correct answer to complete the sentence is option C: "that." This choice is appropriate because it introduces a defining clause that elaborates on the specific difference being mentioned between men and women. Here’s a detailed breakdown of why "that" is the best fit:

In the context of the sentence, the phrase following "that" serves to specify and clarify the important difference in question. The structure "the difference...that..." is commonly used in English to indicate a specific characteristic or quality that distinguishes two subjects. In this case, the distinction is between the body composition of men and women with regard to muscle percentage.

The other options do not fit as well grammatically or contextually.

- A) "is that" suggests a sentence structure that would require a different formal setup, which does not align with the initial clause.
- B) "which is" implies additional, non-defining information rather than a direct clarification of the difference.
- D) "in that" could work but is less straightforward and more idiomatic, potentially adding unnecessary complexity for this sentence structure.

Thus, "that" is the most direct and clear choice to express the intended comparison.