The correct answer is a. Why is the pronoun it correct?
It was not long after the 1930s commenced that such baritone singers as Bing Crosby and Russ Columbo contributed to the popularization of a type of romantic, soothing singing that came to be called "crooning."
a. It was not long after the 1930s commenced that such baritone singers as Bing Crosby and Russ Columbo contributed to
b. Not long after the commencement of the decade of the 1930s, baritone singers such as Bing Crosby and also Russ Columbo decided to contribute in
c. Not long after the 1930s commenced, baritone singers like Bing Crosby and Russ Columbo contributed to
d.Not long after the beginning of the 1930s commencement, baritone singers like Bing Crosby and Russ Columbo had contributed to
e.It was not long after the 1930s commenced that baritone singers such as Bing Crosby and Russ Columbo had contributed in