Temperature is measured by means of a thermometer (温度计). One general form of thermometer depends upon the fact that most solids and liquids expand as their temperature rises. There are one or two exceptions. There is, for instance, a kind of steel called invar (from “invariable”) which does not change its dimensions as temperature changes; it is valuable for making pendulums (钟摆), since, if the length of a pendulum changes, its time of vibration changes. It is also used for making very accurate measuring scales. In both cases, then, changes of atmospheric temperature have no effect if invar is used.
Another exception is that very odd liquid, water, which has many strange properties (特性). As water gets colder it contracts (收缩), which is ordinary behavior, until it reaches the temperature of 30℃. above freezing point. After that, as it gets colder, it expands. This is fortunate---for considering the freezing of a pond. As the water on top gets colder, it shrinks; and so, volume for volume, it becomes heavier and sinks. This goes on until all the pond is at 30℃, but after that, as the water becomes colder it expands. Therefore the colder water stays on top and freezes, covering the pond with ice. If the water went on contracting down to the freezing point, the pond would become a solid block of ice in the end. This would not worry people who live in hot climates, but it would be very serious for those who live in cold climates, especially for those who want to break the ice and catch fish which live in the cold water beneath.
Invar is valuable for making pendulums because _______.

A．it can hardly change its shape or size as temperature changes.

B．it will change its dimensions without the change of temperature.

C．its time of vibration doesn’t change if its length changes.

D．its time of vibration does not change if its length changes.

As water gets colder after reaching the temperature of 30℃. it will _______.

A．contract

B．shrink

C．expand

D．freeze

Which of the following statements is true, according to this passage?

A．Only invar can be used to make a thermometer.

B．Only water can be used to make a thermometer.

C．Both invar and water can be used to make a thermometer.

D．Neither invar nor water can be used to make a thermometer.

The best title of this passage is most likely to be  _____.

A．Temperature Measurement	B．Two Exceptions
C．Uses of Invar	D．Properties of Water