Which of the following description about sound wave is NOT correct.

a. Sound wave can be reflected, absorbed and refracted.

b. Sound wave cannot pass through vacuum.

c. Some animals can hear ultrasound (frequency > 20 kHz).

d. A higher pitch of sound is heard when the source of the sound is approaching because the speed of the sound wave is higher.

e. The intensity threshold of hearing for human is 10^(-12) W/m^2.