Which sound does the symbol "ð" denote?

The symbol "ð," known as the voiced dental fricative, represents the "th" sound found in words like "feather" and "this." This sound is produced by placing the tongue against the upper teeth and vibrating the vocal cords. It is characterized by its voiced nature, meaning that the vocal cords engage during its articulation, differentiating it from the voiceless counterpart "θ," as heard in "three."

In contrast, the other options do not correspond to the "ð" sound. The "sh" sound in option C is represented by the symbol "ʃ" and occurs in words like "shoe," while "zh," as in option D, is related to a different sound represented by "ʒ," found in "garage." Additionally, option B represents the voiceless "th" sound, "θ," as found in "three." Thus, the correct answer effectively captures the unique voicing and articulation associated with "ð."