This is an excellent question and If we see the question stem closely, the question is not exactly a strengthen question, it's an assumption question. why?
Let's have a look:
The association's argument ---What is the association's argument?
-Association thinks that diversity is important in the work force as it has produced new ideas in management, product development, and marketing and will continue to do so.
as it is presented in the passage above would be most strengthened if which of the following were true--So the question stem says: Which of the following options has to be true in order to make association's argument to be true or to make association's argument more believable?
--Heard this sentence somewhere??
...Well revise the first chapter of your assumption notes
<Atleast I did>
(A) The percentage of minority and women workers in business has increased more slowly than many minority and women's groups would prefer.
-- What would the preference of 'many minority and women's group' has to do with association's argument? Out of context
(B) Those businesses with the highest percentage of minority and women workers are those that have been the most innovative and profitable.
--Negate
--"Those businesses with the highest percentage of minority and women workers are those that have
NOT been the most innovative and profitable"...hmm so if the businesses with most minority and women workers are not the most innovative and profitable businesses then association's argument does not stand true. So hold on to this.
(C) Disposable income has been rising as fast as among the population as a whole.
--Disposable income is rising among the population....wow! ...This statement is not even close to what association thinks about the inclusion of minority and women. Out of context.
(D) The biggest growth in the sales in the manufacturing sector has come in industries that market the most innovative products.
--So Biggest Growth in manufacturing was the result of most innovative products...Hmm so were these products suggested by minorities or women? Not sure!.
-Even if you negate this option, the negated option will not make any impact on the association's assertion on minorities and women groups.
(E) Recent improvement in the management practices have allowed many manufacturers to experience enormous gains in worker productivity.
--Improvement in Management Practice ---> Gains in worker productivity
--Were the improvements in management practice result of the inclusion of Minorities/Women? We don't know.
--No impact on Association's assertion on diversity in workforce.
So here you go!...Option B is our answer.