How do proteins become embedded in the membrane of the endoplasmic reticulum?

A)by protein chaperones that insert polypeptides into the ER membrane
B)by splicing of proteins on either side of the ER membrane
C)via stop- and start-transfer sequences that stop and start translocation of a polypeptide through the ER membrane,resulting in transmembrane proteins
D)by post-translational import can results in a transmembrane ER protein
E)via transit sequences that target polypeptides made in the cytosol for the ER membrane