In H. G. Wells's The Time Machine, what is the function of the wells?

They manufacture goods for the Eloi.

They are used to cook Eloi.

They are ventilators for the underworld.

They are Morlock transports.

In H. G. Wells's "The Time Machine", the function of the wells is:

They are ventilators for the underworld.

Its function was mentioned by the Time Traveller when he had found a small, ape-like creature went down to the well and then evolved into two different animals which represent the upper and underworlds. They lived in tunnels ventilated by wells.