Sound waves must have intensity if a person is to hear them.
a. true
b. false

a. True

Explanation:

Intensity is what we commonly call Volume, sound waves with no intensity or volume wouldn´t be hearable by humans, so the statement would be True, Sound waves must have intensity if a person is to hear them. The most usual unit to measure sound intencity is Decibels, and  a person with good ears can hear up to -15 dB.

it was given as a lesson and guide for prayer.