I do not have a pet dog, but I have _____ e-cat at home. [ ]

A. the

B. a

C. an

D. /

受精卵不断进行分裂，发育成胚泡后移到______进一步分裂和分化，形成胚胎，胚胎通过______、脐带从母体中获得所需要的营养物质．