24) B

The paragraph explains in detail about brood parasitism noted in the three groups of birds. However, it uses brood parasitism as an example of convergent evolution. It also states this in the 4th sentence.

Option A is not correct because the main argument is not only about cuckoos, cowbirds and honeyguides avoiding raising young chicks. The argument is more about explaining convergent evolution by using brood parasitism as an example.
Similarly with option C, the main argument is not about eggs with thicker shells.

Option D is wrong because nothing is mentioned about life adaptation.