The concept of divided the octave into 12 tones which to avoid unpleasant harmonies.

The answer to the question presented above would be 'equal temperament'. The concept of equal temperament divide the octave into 12 tones. This helps avoid the harmonies to be deemed unpleasant when the music is played.

What do you mean by this?

Iwould go with write exactly two extra paragraphs to point out additional information. but the keyword "exactly" throws me off. leads me to believe it's d. go with your gut feeling. either "write exactly two extra paragraphs" or "none of these".