Which intrusive feature may start as a sill but, as more magma builds, it pushes upward like a lens? laccolith batholith igneous rock extrusive igneous rock

Laccolith is the answer.

The same way as sills, laccoliths form from a more viscous magma which collects as lens-shaped mass that arches the overlying structure upward. They can be recognized because of the dome they form at the surface.