Hey there!
Here is your answer:
The proper answer to this question is option A "musical note".
Reason:
A musical note anything can hear unless the person or animal is def.
Also...
Its not options B, C, or D because they are made in order to have something specific to here. For example the dog whistles was made for dogs and also only dogs could hear the whistles.
If you need anymore help feel free to ask me!
Hope this helps!
~Nonportrit