Which one of the following indicates a drop in temperature?

A. The alcohol in a thermometer expands.

B. The column of liquid in a thermometer moves up three degrees.

C. The brass on a bent bimetallic strip is on the outside curve.

D. A bimetallic strip bends so that the steel is on the outside curve.

Among the choices, the correct answer is D. "A bimetallic strip bends so that the steel is on the outside curve."

A bi-metallic strip is composed of 2 metals with different thermal coefficients. One side (usually brass) expands much faster than the other side (usually iron or steel). When brass is on the outside curve, then it means that the temperature has risen. If steel is on the outside curve, then it means that the temperature has dropped.