Alternate determination of muliple BOM's

Hi,

We are maintaining multiple BOM's. We have also maintained muliple production versions. Selection setting in material master is kept as 2(by production version). No when we run MRP what is the criteria of selecting a specific production version considering all production versions meets requirements of lot size & validity.

Secondly is it a manual process or automatic process.

We are using REM.

regards,

Mohit