B, C, and D are the second, third, and fourth letters of the English alphabet. Each letter has its own unique sound and is used to form words. For example, B represents a voiced bilabial stop, while C can represent a hard sound as in "cat" or a soft sound as in "cereal." D is a voiced alveolar stop. In addition to their phonetic roles, B, C, and D are also used in various systems, such as grading. In academic contexts, B typically indicates good performance, C represents average performance, and D signifies below-average performance.