Standard Costing in bills alternatives

Hi,

We want to handle discrete manufacturing standard costing, but we have a question:
Item A = $ 5
Item B = 8
We have two bill of materials for a product manufactured XYZ:
Bill M has the component item A
Bill M1 has the component item B
Therefore, the cost of the product will have two different costs XYZ.
My question is this:
What configuration should be done to make the system freeze every bill of materials (M and M1) so that when a production order is made and the bill of materials is chosen, the system considers the standard cost of the product