When building a pick ray through GluUnproject...

I don’t know if it’s correct to ask about GLU on the OpenGL boards… anyway:

GluUnproject takes two input matrices: modelview, and projection.
No problems with the projection matrix, some doubts on modelview.

I currently have a camera matrix, and a various matrix for the several objects I am rendering.

When using gluunproject to build a picking ray, what should I use ad modelviewmatrix? The one which derives from camera matrix only (thus, camera matrix itself), or the product of camera matrix and the single object I am going to test againist?

Thanks in advance,