How are musical instruments grouped? a: by their frequency b: by the wavelengths they produce c: by what they are made of d: by how they produce pitch

Musical instruments are grouped by how they produce the pitch.

Pitch is the highness or lowness of a tone.

the skeletons of most mammals reach a certain size and then stop growing. however, many animals, including some mammals, keep growing throughout their lives. kangaroos, for example, just keep growing and growing until they die. also, the longer an animal lives the greater the chance it might catch some deadly disease.