Question

Which of the following sequences will result in two different species?

Allopatric becomes sympatric; species interbreed and are subjected to postzygotic RIMs.
Sympatric become allopatric; species interbreed, and all offspring are fertile.
Sympatric becomes allopatric; species interbreed; reproductive isolation never occurs.
Allopatric becomes sympatric; species interbreed; reproductive isolation never occurs.
Allopatric becomes sympatric; species interbreed, and all offspring are fertile.