Bats use high frequency. Whenever somebody says a quantity is "high", you have to ask "compared to what ?". In this case, it's compared to human hearing ... we can't hear bats at all, or if we can, it just sounds like a 'click'.
Bats use high-frequency sounds for echolocation, which are typically above 20 kHz, allowing them to effectively navigate and hunt in the dark. Humans cannot hear these ultrasonic sounds, which gives bats an advantage in their environments. Therefore, the correct answer to the question is C. high frequency.
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