We see that the bird , by spinning, create upwelling currents, and the plankton it eats is usually concentrated below the surface. It is logical to suspect that the birds spins for this reason, but it may be that the bird spins for other reasons. If E were false, i.e. if the bird spun even when it has plankton within easy reach, we should suspect that the bird spins for some other reason. If the bird has all of the food it wants, why should it waste energy spinning?
Valerie wears high-heeled shoes when she goes to discoteques, even though she is more comfortable in running shoes. Men thus think that she is really taller than she is, and men are known to be attracted to tall women. Is it clear that Valerie wears high-heeled shoes to attract men? What if it's true that she wears high heels even when she visits her parents in a nursing home where the staff is entirely female?
Kevin Armstrong
GMAT Instructor
Gmatclasses
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