Any medical test will sometimes fail to detect a condition when it is present and indicate that there is one
when it is not.
(A) a condition when it is present and indicate that there is one
(B) when a condition is present and indicate that there is one
(C) a condition when it is present and indicate that it is present
(D) when a condition is present and indicate its presence
(E) the presence of a condition when it is there and indicate its presence

what type of pronoun is one ? when could "one " be used ?
one in A and B is wrong