Which of the following would be LEAST likely to lead to speciation?

As a result of rising ocean levels, an island that once contained a homogenized population of arabidopsis has now undergone genetic drift. The island has been divided into two parts, separated by a significantly large body of water. What is likely to have happened to result in two genetically different populations that can no longer reproduce?

A certain type of flower used to grow on both sides of the Amazon River. However, over time, the salinity of the soil on the north side grew significantly, while the salinity on the south side stayed the same. Over time, the flowers on one side became unable to reproduce with the flowers growing along the opposite bank because their offspring could not survive in the saline conditions; however, these plants were formerly of the same species.

What type of speciation is described?

Which of the following is not a type of speciation?

A species of fruit fly that traditionally inhabits the western slope of a mountain was blown by the wind to reach the eastern side of the mountain. Over time, the fruit fly population on the eastern side of the mountain lost its ability to mate with the western fruit flies when they encountered each other. This is an example of which type of speciation?

A certain type of flower used to grow on both sides of the Amazon River. However, over time, the salinity of the soil on the north side grew significantly, while the salinity on the south side stayed the same. Over time, the flowers on one side became unable to reproduce with the flowers growing along the opposite bank because their offspring could not survive in the saline conditions; however, these plants were formerly of the same species.

What type of speciation is described?