A. Although many theories exist, the reason for Amelia Earhart's disappearance remained a mystery. B. Although many theories exist, the reason for Amelia Earhart's disappearance remains a mystery. C. Although many theories exist, the reason for Amelia Earhart's disappearance is remaining a mystery. D. Although many theories are existing, the reason for Amelia Earhart's disappearance remains a mystery.
