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Expression of IdeasMediumExplaining why bridges have expansion joints

Expression of Ideas practice question

While researching a topic, a student has taken the following notes: - Steel expands when it is heated. - A long steel bridge can lengthen by tens of centimetres on a hot day. - Expansion joints are gaps built into the bridge deck. - The gaps close as the bridge lengthens, so the deck does not buckle.

The student wants to explain why bridges have expansion joints. Which choice most effectively uses relevant information from the notes to accomplish this goal?

  1. A. Bridges have expansion joints because their steel lengthens in hot weather, and the joints' gaps close to absorb that growth instead of letting the deck buckle.Correct
  2. B. A long steel bridge can lengthen by tens of centimetres on a hot day.
  3. C. Expansion joints are gaps built into a bridge deck.
  4. D. Expansion joints allow a bridge to carry heavier loads.

Answer: A. Bridges have expansion joints because their steel lengthens in hot weather, and the joints' gaps close to absorb that growth instead of letting the deck buckle.

The goal asks WHY. Choice A gives the cause and what the joints prevent.

Why the other answers are wrong

B. A long steel bridge can lengthen by tens of centimetres on a hot day.
A fact about expansion with no mention of the joints.
C. Expansion joints are gaps built into a bridge deck.
A definition, not a reason.
D. Expansion joints allow a bridge to carry heavier loads.
Nothing in the notes concerns loads.

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