GMAT Sentence Correction (SC) | Re: Until Berta and Ernst Scharrer established the concept of

Until Berta and Ernst Scharrer established the concept of neurosecretion in 1928, scientists believed thateither 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