We live in the cenozoic era, and scientists know more about this era and the epochs it's divided into than any other time period. why is this?

The Cenozoic era is the most recent era which still lasts. It is the era about which the scientist have by far the most knowledge. The reason why this era is much better studied and known by the scientists is exactly that it is the most recent one. The fossils are there in abundance as they did not had enough time to totally dissolve. The rock layers formed in this period are largely kept, and very little of them have been destroyed. The continents have moved of course, but it is easily traceable and in much lesser extent when compared with longer periods of time. The events that happened in this era are much recent, so their leftovers are abundant, as well as easier to study and find. All of this have resulted in much larger database, and significantly greater knowledge about this era than any other before it.

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.

if your own plato the answer is b. the fern transitioned from sporophyte generation to gametophyte generation.