A(n) blank is a pure substance that can't be broken down into simpler substance by chemical or physical means

e                   for effort

i think it’s true but i’m not sure

i'm not sure i completely understand your question, but i will do my best.

i think the answer you are looking for is sequence. (see below)

a repeated melodic fragment would be best defined as repetition, while repeated chords (different or the same) could be a chord progression. however, you then mentioned the chord and melodic fragment beginning on higher or lower pitches, in that case, the answer could be best defined as a sequence. the definition of a sequence is as follows: "the restatement of a motif or longer melodic (or harmonic) passage at a higher or lower pitch in the same voice."

let me know if this !

i think it's about 10 mins.

actually i think that's wrong, but i don't know how to delete this.

but who knows it might be right.