A humble request – Please give KUDOS if you like the explanation.
The answer is E.
A historic composer for Western music, Mozart’s Serenade No.13 is to the classical period what Vivaldi’s The Four Seasons is to the Italian Baroque period.
Let us first dissect the sentence.
A historic composer for Western music, - This part of the sentence acts as a modifier that modifies Mozart
Mozart’s Serenade No.13 is to the classical period what Vivaldi’s The Four Seasons is to the Italian Baroque period.
x is to y what a is to b – This is the correct idiom
A. Mozart’s Serenade No.13 is to the classical period what
This is correct idiomatic usage.
But modifier is incorrect
B. Mozart’s Serenade No.13 is to the classical period like
x is to y like a is to b – This is the incorrect idiom
C. Mozart’s Serenade No.13 is to the classical period just as
x is to y just as a is to b – This is the incorrect idiom
D. Mozart wrote Serenade No.13 that is to the classical period similar to
x is to y what a is to b – This is the correct idiom
similar to is incorrect
E. Mozart wrote Serenade No.13 that is to the classical period what
x is to y what a is to b – This is the correct idiom