Which one of the following indicates a drop in temperature?

a. the column of liquid in a thermometer moves up three degrees.
b. the alcohol in a thermometer expands.
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

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

When something has an increased temperature, its volume will expand. Then, if the temperature drops, its volume should be smaller. From there option A and B are out since the liquid in thermometer is expand or move up.

When you put two kinds of different metal with a different coefficient of thermal expansion, the outer curve metal will be the one with lesser coefficient when temperature drop. Since the question about drop in temperature then the metal should be bend
Brass will expand 1.5 times more than the steel so the outer curve would be the steel.