Bats use ultrasound in echolocation. this sound is characterized by
low frequency
low amplitude
high frequency
high amplitude

The correct answer is "high frequency".

Explanation:

The normal range of frequency of human being is from 20 Hz to 20,000 Hz.

Bats uses ultrasonic wave. The range of this wave is more than the audible frequency of the human. It is more than 20,000 Hz. It cannot be heard by human.

Bats use ultrasound in echolocation. It emits ultrasonic wave then this wave reflects back from the obstacle or prey which help it to locate it prey. Ultrasonic wave is a high frequency wave.

Therefore, Bats use ultrasound in echolocation. This sound is characterized by  high frequency.

it becomes positively charged by charging it