Answer: Ternary Form
Explanation: Ternary Form is a musical form that introduces an idea, (A) then introduces a contrasting idea, (B) then returns back to the original musical idea, often copying the first phrase how it was, maybe including some slight variation in the harmony or rhythm. A good example of a simple piece written in Ternary Form is Mozart's Andante in E-Flat Major.
I think the answer is 20 but I am not sure,I heard about 15 and 25
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Rythmn and Harmony are the basic elements.
Not sure if you're asking for the scale itself but i'll give it to you anyway.
D Major has 2 sharps. F and C.
Scale: D , E , F# , G , A , B , C# , D