An Ordinary Mercury Thermometer at Room Temperature Is Quickly Placed

An ordinary mercury thermometer at room temperature is quickly placed in a beaker of hot water. The mercury column is observed to drop slightly before it rises to the final equilibrium temperature. Which one of the following statements is the best explanation for this behavior?

A) The glass envelope expands before the heat reaches the mercury.
B) The expansion coefficient of glass is larger than that of mercury.
C) Both the mercury and the glass initially expand, but at different rates.
D) Initially, the mercury contracts.
E) Initially, the glass envelop contracts.