Researchers know the role of some myokines in the human body, __ there are still many more that are still a mystery A. But B. So C. Because D. After

A. is your answer. have a good one.

The correct answer for this question is that a statement that can be proven by observation or measurement is known as a fact. The other possible answers here simply refer to idea that different individuals can place value on, but that are not necessarily known to be true.