This seems to be a wrong question and it is among the beat the gmat practice questions.Kindly look into it guys 
As per the explanation in OG12 for the sentence correction question number 14 - the explanation clearly mentions that "'Although' typically is a sub ordinate clause construction and it requires a subject and verb"
As per the explanation in OG12 for the sentence correction question number 14 - the explanation clearly mentions that "'Although' typically is a sub ordinate clause construction and it requires a subject and verb"
