Two identical ambulances with loud sirens are driving directly towards you at a speed of 40 mph. One ambulance is 2 blocks away and the other is 10 blocks away. Which of the following is true? 
[Note that pitch = frequency.]a) The siren from the closer ambulance sounds higher pitched to you. b) The siren from the farther ambulance sounds higher pitched to you. c) The pitch of the two sirens sounds the same to you. d) The siren from the farther ambulance sounds higher pitched, until the
 closer ambulance passes you.