Which is the most likely explanation for the membrane's asymmetrical nature?

Cell membrane proteins are determined as the membrane is being packaged in the ER and Golgi.

or

The two sides of a cell membrane face different environments and carry out different functions.

Iam not sure but to me it with be a or dsorry if i was late! hope this ! : )if you really want me to find out the answer that is correct tell me and i will do more research but the a or d makes sense to me.