Sentence Correction (SC) | Re: Charles Lindbergh, for his attempt at a solo transatlantic flight, was

Hellohimanshu0123 ,

We hope this finds you well.

To answer your query, yes; "therefore" is a subordinate clause marker, so "he therefore refused to carry even a pound of mail" is a dependent clause.

Further, the use of "being" is not incorrect in Option B, but it is needlessly indirect.

We hope this helps.
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