685. The 19th-century proponents of the school of thought known as mechanism held that life process are not the products of some mysterious life force, but are the same chemical and physical processes that operate in inorganic systems, which is still a subject of debate between biologists today.

(A) systems, which is still a subject of debate between

(B) systems, which are still debated between

(C) systems still debated among

(D) systems, a theory still debated by（D）

(E) systems, a theory still debated between

答案a.b.e都不可能,但較讓我疑惑的是"a theory"是同位語吧?那是指代誰呢？按照句意判斷,應該也不可能是指代"inorganic systems" thanks