Most metals expand when heated and contract when cooled. A few alloys, however, behave in the opposite way over certain temperature ranges: Invar, an iron-nickel alloy, contracts as it warms before resuming ordinary expansion above a threshold temperature. This unusual behavior makes Invar valuable for precision instruments.
Which choice best describes the function of the second sentence in the text?
- Acheck_circle
It introduces a counterexample whose unusual behavior is the focus of the rest of the text.
- B
It defines the term 'alloy'.
- C
It supports the general claim about metallic expansion.
- D
It traces the historical discovery of metals.
Explanation
Invar's contraction-on-warming is offered as a counterexample that the third sentence develops. B captures the counterexample function.