Even if the researchers made their hypothesis before analyzing the database, (A) fails to show how the results of the analysis support that hypothesis. So, (A) doesn’t strengthen the argument.

This weakens the argument by providing an alternative hypothesis to explain the results of the analysis. If highly educated residents are more likely to eat curries, it makes sense that those residents who eat curries also scored higher on cognitive tests.

We already know that regular curry consumption is linked to higher cognitive test scores, especially among elderly Indian Singaporeans. Also, since the researchers are only analyzing a sample of elderly Singapore residents, the eating habits of other residents are irrelevant.

Irrelevant— the researcher’s hypothesis is based on data from elderly Singapore residents. It doesn’t matter what residents of most other countries eat.

This somewhat strengthens the hypothesis because, if the link between high curry consumption and better cognitive scores is strongest among elderly Singaporeans of Indian descent, and Indian curries have much more turmeric, it suggests that turmeric may slow cognitive decline.