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Sorry! Wrong!

The correct answer is:

D. None of them.

No planet could be seen without optical aid if all the planets we see in the sky were as far as Pluto's mean distance from the Sun. The sunlight striking them would be too weak, and that light would spread out too much en route to Earth.

The two brightest planets would be the two largest, Jupiter and Saturn; but even they would be sixth and seventh magnitude, respectively--visible through binoculars, but not to the naked eye. The other planets would be fainter, and Mercury would be fainter than Pluto.

Why does Pluto look as faint as it does? Not because it's small. Because it's far away!

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