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24. Many major scientific discoveries of the past were the product of serendipity, the chances discovery of valuable findings that investigators had not purposely sought. Now, however, scientific research tends to be so costly that investigators are heavily dependent on large grants to fund their research. Because such grants require investigators to provide the grant sponsors with clear projections of the outcome of the proposed research, investigators ignore anything that does not directly bear on the funded research. Therefore, under the prevailing circumstances, serendipity can no longer play a role in scientific discovery.

Which one of the following is an assumption on which the argument depends?

(A) Only findings that an investigator purposely seeks can directly bear on that investigator’s research.

(B) In the past few scientific investigators attempted to make clear predictions of the outcome of their research.

(C) Dependence on large grants is preventing investigators from conducting the type of scientific research that those investigators would personally prefer.

(D) All scientific investigators who provide grant sponsors with clear projections of the outcome of their research receive at least some of the grants for which they apply.

(E) In general the most valuable scientific discoveries are the product of serendipity.

仔细分析，A是对的，但B为什么不对，B不是说明过去和现在的差异吗，请指教！