<image>There are 2100 students in a school. In the "Civilized Behavior Pioneer" campaign, the school offers five school-based courses: "Law, Etiquette, Gratitude, Environment, and Mutual Help." Each student must choose and can only choose one course. To understand students' enrollment intentions, the school randomly surveyed 100 students and created the following statistics table:
(1) In this survey activity, the type of survey the school conducted is __________ (fill in "census" or "sampling survey").
(2) a = __________, b = __________, m = __________.
(3) If a "school-based course enrollment intention pie chart" is to be drawn, the central angle of the pie corresponding to "Etiquette" courses is __________ degrees.
(4) Please calculate the approximate number of students in the whole school who chose the "Gratitude" course.
