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.

laccolith

Explanation:

The laccolith is the sheet type of intrusive rock that has been injected within or between the layers of the sedimentary rocks and the pressure of the magmas is higher enough that the magmas are forced upwards and are folded in a dome-like a mushroom structure. This little structure can grow in about a few months when formed with a single magma injections as these features tend to form at very shallow depths.