GMAT Sentence Correction (SC) | At a time when Queen Anne was so ill that she had to be

At a time when Queen Anne was so ill that she had to be hoisted up between floors of her palace, the Whigs had seized upontheir best gambit in the war between the parties and, hovering nervously, Defoe was between upholding the ministry's commitment to the Protestant succession and his own sense of how vital such a commitment must be.
(A) their best gambit in the war between the parties and, hovering nervously, Defoe was between
(B) its best gambit in the war between the parties,