Discussion
Surface area of sphere is
Answer: B
A sphere's surface area is
\[ S = 4\pi r^{2} \]
Note that it is exactly four times the area of a great circle (\( \pi r^{2} \)) - the flat disc you would get by slicing the sphere through its centre.
The distractors are all real formulas from elsewhere: \( 2\pi r \) is the circumference of a circle, and \( 2\pi r^{2} \) is the curved surface of a hemisphere. A surface area must be proportional to \( r^{2} \), which rules out \( 2\pi r \) on dimensional grounds alone.
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