2 Let y =f(t), t > 0, be the solution to initial value problem 3)" = a yz, y(0) =y0 0 is a constant. Which one of the following statements is true? O a) yitj is decreasing and its graph is concave up for all t 2 O O b) ya) is decreasing for all t Z 0. There exists :1 > 0 such that the graph of y(r) is concave down when 0 :1. O C) y(t) is increasing and its graph is concave up for all t 2 O Q d) yltj is increasing and its graph is concave down for all t2 0 O e) y(i') is increasing for all 1' Z 0. There exists {1 > 0 such that the graph ofy(r) is concave up when 0