The conclusion in the argument is:
"Clearly, sales of the Daisygen rose will outnumber those of the original rose species."
A. The genes which were spliced into the rose are not also responsible for the onion's tearing effect. argument doesn't mention any negative consequences like smell or tearing. While this might affect consumer acceptance, it's not assumed in the argument, so not necessary for the conclusion to hold.
B. Consumers are interested in a flower that will last longer. -CORRECT
This is crucial. The conclusion hinges on the idea that the Daisygen rose’s longer life makes it more appealing, and will therefore sell more. But that only makes sense if consumers value longevity.
This is a necessary assumption—if consumers don't care about how long a flower lasts, then the whole sales advantage disappears.
C. Plastic flowers have not affected the import and export of natural flowers.
This may affect overall flower industry trends, but the argument is comparing sales of Daisygen roses vs. original roses, not plastic vs. real. Not necessary.
D. Although extremely popular, the original rose was not the highest selling flower species of all.
Irrelevant. The argument is not comparing roses to other flower species, only Daisygen roses vs. original roses.
E. A longer expiration period will allow importers more time for delivery of the Daisygen roses.
That’s a benefit to importers, but the conclusion is about sales, not logistics. Importers may appreciate the benefit, but it doesn't mean more sales unless consumers want the product. Not a necessary assumption.