Question

what is one important characteristic of modern landfills?
large fans to reduce the smell
a plastic liner

Explanation:

Modern landfills are designed to prevent environmental contamination. A plastic liner is a key component as it helps to contain leachate (liquid from waste decomposition) and prevent it from seeping into the soil and groundwater. Large fans to reduce smell are not a fundamental or defining characteristic of modern landfills compared to the essential role of the plastic liner in environmental protection.

Answer:

A plastic liner