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.
