【正确答案】 C

【答案解析】 Grammatical Construction; Idiom; Parallelism
   As worded, this sentence opens with a dependent clause (a clause that cannot stand on its own), which requires a main clause (also known as an independent clause) to complete the sentence; however, there is no main clause. Also, given the placement of as before both, the as before a lyricist is incorrect. It would be acceptable to write as both a vaudeville performer and a lyricist or to write both as a vaudeville performer and as a lyricist, it is not acceptable to mix the two forms, as is done here.
   A   The dependent clause, While... Broadway musicals, is followed by a participial phrase rather than a main clause and is therefore ungrammatical. Furthermore, the word as before a lyricist violates the parallel structure required by the phrase both... and.
   B   The construction as both a performer and writing lyrics is incorrect. Also, like (A), this version of the sentence does not supply a main clause.
   C   Correct. Unlike (A) and (B), this version has a main clause. Also, unlike the other version, it correctly uses the both x and y form.
   D   Although this version does supply the main clause anticipated by While  its use as both a vaudeville performer as well as writing lyrics is incorrect.
   E   This version's use of both x as well as y instead of both x and y is incorrect. It also introduces an inexplicable past perfect verb, had... enjoyed, in the main clause.
   The correct answer is C.