At present, students from a certain school are selected to participate in the "Mathematics", "Physics" and "Chemistry" competitions in senior high school, and at least one person from each subject participates in the subject competition, so the number of people in different competition schemes is () A.B.C.D.B

Classify first and then complete it step by step. Firstly, four students are selected from five students, and one student is required to participate in each subject, which is equivalent to a grouping problem. At the same time, each student is limited to one subject. So it is divided into three groups, arranged by species, and obtained by the principle of step-by-step counting = 180, so B is chosen.