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Expression of IdeasMediumExplaining a purpose

Expression of Ideas practice question

While researching a topic, a student has taken the following notes: - Ships are painted below the waterline with a paint containing copper compounds. - Copper deters barnacles and weed from attaching to the hull. - Growth on a hull slows a ship and increases its fuel use. - The copper compounds give the paint its red colour.

The student wants to explain why ships are painted with copper-based paint below the waterline. Which choice most effectively uses relevant information from the notes to accomplish this goal?

  1. A. Ships carry copper-based paint below the waterline because copper deters the barnacles and weed that would otherwise slow the ship and raise its fuel use.Correct
  2. B. The copper compounds give the paint its red colour.
  3. C. Ships are painted red below the waterline.
  4. D. The red paint makes ships easier for other vessels to see.

Answer: A. Ships carry copper-based paint below the waterline because copper deters the barnacles and weed that would otherwise slow the ship and raise its fuel use.

The goal asks WHY. Choice A gives the reason and its consequence.

Why the other answers are wrong

B. The copper compounds give the paint its red colour.
This explains the colour, not the purpose.
C. Ships are painted red below the waterline.
This states what is done, not why.
D. The red paint makes ships easier for other vessels to see.
Visibility appears nowhere in the notes — and the paint is below the waterline.

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