problem in material selection in bom

Hi,

we have finish material A,semi finish B, raw material C1,C2,C3.

we have created material BOM for semi finish B.

material usage alternative BOM component.

B 1 1 C1, C2.

B 1 2 C3.

I created bom for finish material A using semi finish B mentioning alternative bom 2. it is not picking the component which is there in alternative BOM 2 i.e. C3.

in cs11, it is showing only C1, C2.

Can you solve this. it's very urgent.

thanks/regards

vish