Draw a timing diagram with the following signals (where [t1,t2] is the time interval starting at t1 and ending at t2):

a. signal A is stable [0,10], changing [10,15], stable [15,30]

b. signal B is 1 [0,5], falling [5,7], 0 [7,20], changing [20,30]

c. signal C is changing [0,10], 0 [10,15], rising [15,18], 1 [18,25], changing [25,30]