(B) Polio, although eradicated in the United States, it still continues elsewhere and can be

(C) Although still continuing elsewhere, polio has been eradicated in the United States and could be

(D) Although having been eradicated in the United States, polio still continues elsewhere and is capable of being

(E) Although eradicated in the United States, polio continues elsewhere and could be

答案是E，但是为什么continues 可以和could并存？