Chips thought often, as he sat by the fire at Mrs. Wickett's: I am probably the only man in the world who has a vivid recollection of old Wetherby.

Explanation

The incorrect adverb placement is in option A ("Often")."Often" is an adverb that describes the frequency of Chips' thoughts. However, in the original sentence, it is incorrectly placed before the verb "thought." Adverbs of frequency like "often" typically come after the verb they modify in English sentences.