Spending on research and development by United States businesses for 1984 showed an increase of about8 percent over the 1983 level. This increase actually continued a downward trend evident since 1981 – whenoutlays for research and development increased 16.4 percent over 1980 spending. Clearly, the 25 percent taxcredit enacted by Congress in 1981, which was intended to promote spending on research and development,did little or nothing to stimulate such spending.

The conclusion of the argument above cannot be true unless which of the following is true?

【选项】Had the 1981 tax credit been set higher than 25%, business spending for research and development after 1981 would have increased more than it did.