A) Many argue that a high number of absences result in lower grades; however, the studies making these connections do not consider the educational reasons students might miss school.
This is the best choice for a few reasons. The first being that it clearly connects the claim to the counterclaim by talking about the issue of absenteeism in schools in regards to grades. Another reason this is a better choice than the others is that it maintains the formal tone throughout the entire sentence. Some of the other options begin to lose the formal tone that is required of an argumentative essay.