and thus后面的句子省略的主语谓语,是否意味着前面的谓语动词一定是be动词?

Until Berta and Ernst Scharrer established the concept of neurosecretion in 1928, scientists believed that either cells secreted hormones, which made them endocrine cells and thus part of the endocrine system, or conducted electrical impulses, in which case they were nerve cells and thus part of the nervous system.

(A) either cells secreted hormones, which made them

(B) either cells secreted hormones, making them

(C) either cells secreted hormones and were

(D) cells either secreted hormones, in which case they were

(E) cells either secreted hormones, which made them             

选了E,,,感觉D很罗嗦啊...

不过我后来看到未划线部分有and thus,知道这里肯定省略了和前面一致的主语,但是把E放进去,也是可以解释得通的呀......是否这时省略的谓语动词一定预示着前面出现了be动词呢?

请大牛们看看~~~~~~

平行结构mm要注意对称，有没有看到未划线部分的in which case ？

另外thus是连词，你可以不看他，要简单说的话，应该是and连接的句子，如果主谓相同省略主谓