Which one is wrong?

Despite its cutural importance, the Daily Gazette lost 70 percent of its subscribers since1920


and, by 1955, was losing as much as 2000000 dollars a year. No Error


The correct answer is B, but I choose C. What's wrong with B? And I do not know why C uses past continuous tense.
Because of the phrase of duration, 'since 1920', B should read 'has lost'. The past continuous in C merely emphasizes the continuous loss of money (which, at $200/year, seems quite minuscule!)
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Should it read "has lost" or "had lost"? I know the word "since 1920" ... but we have to pay attention to the "was losing" too. So I wonder, which one is the correct one has lost or had lost? Thanks for your help!
You're absolutely right—had lost. Lucky I wasn't taking the test!