<em>Australian tourists is a proper noun and the Harry's elephant is aslo while hippos is common noun.</em><em> </em>
The right answer here would be A - the phrase 'modulate your voice'
refers to a need to vary your voice's properties. Modulating means
changing the pitch or tone, and can be used referring to one's voice, or
to an instrument. You can modulate both up or down, and this usually
involves changing the key signature in which you are playing or singing.
This sentence is grammatically correct but it is not adverb phrase it is Syntax