The role of envelope detector in an AM receiver is to

• retrieve the message signal

• rectify the AM signal

• modify the AM signal

• modulate the message signal

For commercial telephonic communication, the frequency  range for speech signals is

• 50 Hz to 1000 Hz

• 3000 Hz to 4500 Hz

• 300 Hz to 3100 Hz

• 5000 Hz to 6500 Hz