Explanation:

When determining the conservation status of a species, the International Union for Conservation of Nature (IUCN) Red List criteria are used. These criteria consider factors such as population size, decline rate, and distribution to classify species into different categories of conservation concern.

In this scenario, the species has experienced a 90 percent decline over 10 years or three generations. Based on this information, the correct classification would be "critically endangered."

Reasons for the classification:

1. Decline rate: The species has experienced a significant decline of 90 percent over a relatively short period of time (10 years or three generations). This rapid decline indicates a severe threat to the species' survival.

2. Population size: While population size alone is not the sole determinant of a species' conservation status, a 90 percent decline suggests that the species may have a small remaining population or a limited geographic range.

3. Impact on reproductive capability: The decline occurring over three generations indicates that the species is unable to reproduce at a rate that can keep up with the mortality rate. This further highlights the critical situation faced by the species.

4. Threats to survival: The significant decline observed suggests the presence of severe threats to the species. These threats could include habitat loss, pollution, overexploitation, or other factors that are causing the rapid decline.

5. Conservation actions: The critically endangered classification signifies the urgent need for conservation actions to prevent the species from further decline and potential extinction. These actions may include habitat protection, captive breeding programs, population monitoring, and reducing threats to the species.

Based on the above factors, the 90 percent decline over 10 years or three generations qualifies the species to be classified as "critically endangered" according to the IUCN Red List criteria. This classification highlights the urgent need for immediate conservation efforts to save the species from extinction.