Which of the following letters has a counter?

The letter that has a counter is the lowercase "g." In typography, a counter is defined as the enclosed or partially enclosed space within a letterform. For "g," the counter is the inner space formed by the loop of the letter, which is encircled by the strokes of the letter. This characteristic distinguishes it from letters like "a," "b," and "m," which do not feature a fully enclosed area.

In "a," the bowl is open at the top, thus it does not have a complete counter as seen in the lowercase "g." The letter "b" contains a loop, but it does not form a complete enclosed area that qualifies as a counter. "M" is a more angular letter, lacking any enclosed regions altogether. As such, the lowercase "g" stands out because it uniquely possesses a defined counter, contributing to its distinctiveness in both form and structure.