In two to four paragraphs, explain what happened musically as britten introduced the orchestral instruments:

-- Unless I miss my guess, the phrase "In two to four paragraphs,
explain ..." sounds like you want somebody to write a nice essay
for you, which you will then write your name at the top of and hand
it in as your own work.  Are you sure you want to adopt this process
as a substitute for actually learning stuff ?
 
-- Sadly, you can probably forget about offering 5 points and getting
two to four paragraphs in return.

-- Another hunch of mine:  You're referring to the "Young Person's
Guide to the Orchestra" ... a fugue and variations based on the
Rondeau from Henry Purcell's incidental music to Aphra Behm's
Abdelazar, composed by Benjamin Britten in 1946 for elementary
music education.  The subject may not be too familiar to the people
who like to hang out here in the <Physics> category.  You might
stand a better chance if you post the question again in <Arts> or
even <Social Studies>.  I don't know of a way to 'move' a question
on , so you'll have to actually post it again ... and this time,
see if you can spare a few more points for an answer.