When a membrane protein is radioactively labeled during synthesis and followed through the various organelles in the secretory pathway,all the radioactivity is concentrated in the cis-Golgi apparatus six hours after the protein synthesis.This suggests that the protein

A)was imported directly into the cis-Golgi posttranslationally.
B)contains a KDEL sequence near its C-terminus.
C)has a membrane-spanning domain length equals the thickness of the cis-Golgi membrane.
D)has a mannose-6-phosphate tag.
E)is misfolded and being degraded in the cis-Golgi.