In learning theory, receptivity is defined as the ability of students to understand a complex concept. Receptivity is highest when the topic is introduced and tends to decrease as time passes in a lecture. Suppose that the receptivity of a group of students in a mathematics class is given by g(t) = -0.2tz + 3.1t + 32 where t is minutes after the lecture begins. (a) At what rate is receptivity changing 15 minutes after the lecture begins? (b) Write a sentence that explains the meaning of your answer in part (a). O Because g(t) is positive, the students' receptivity is increasing. Because g'(t) is negative, the students' receptivity is decreasing. O Because g(t) is positive, the students' receptivity is decreasing. Because g'(t) is negative, the students' receptivity is increasing