Eskers and Drumlins are features, formed by

Answer: (d) Glacial action

Eskers (ridges of meltwater gravel) and drumlins (oval hills of till) are glacial deposits.

The idea

Ice landscapes contain deposits made both by moving ice and by meltwater associated with it. The shape and sorting of the deposit reveal which agent did the detailed work. A sinuous gravel ridge and a streamlined mound belong to the same glacial setting but form differently.

Why the others are wrong

(c) Wind makes dunes, not eskers.

The trap

Eskers form from meltwater streams, so (a) tempts — but under a glacier.

Elimination technique

An esker may involve flowing meltwater, but it belongs with the drumlin in a glacial landscape. The paired features make (d) the suitable broad agent, rather than ordinary river action.

Also know

Eskers are winding ridges of sorted sand and gravel deposited by meltwater, often in channels beneath ice. Drumlins are streamlined hills shaped beneath moving ice, commonly involving till. Moraines mark accumulated glacial debris; outwash plains contain meltwater-sorted deposits. Cirques, U-shaped valleys and hanging valleys are erosional members of the same family.