The correct answer is: A. Cainozoic era
The Cainozoic era is the longest era of the classification of the history of Earth. It is also known as the Cenozoic era. It began 66 million years ago, with the extinction of the dinosaurs, and continues to the present day. The Cainozoic era is divided into three periods: the Paleogene, the Neogene, and the Quaternary.
The Paleogene period lasted from 66 million to 23 million years ago. During this time, the first mammals and birds evolved. The Neogene period lasted from 23 million to 2.6 million years ago. During this time, the first primates and humans evolved. The Quaternary period began 2.6 million years ago and continues to the present day. During this time, humans have evolved and spread throughout the world.
The Pre-Cambrian era is the second longest era of the classification of the history of Earth. It lasted from 4.6 billion to 540 million years ago. During this time, the Earth formed and cooled, and the first life forms evolved. The Palaeozoic era is the third longest era of the classification of the history of Earth. It lasted from 540 million to 252 million years ago. During this time, the first fish, amphibians, reptiles, and mammals evolved. The Mesozoic era is the fourth longest era of the classification of the history of Earth. It lasted from 252 million to 66 million years ago. During this time, the dinosaurs evolved and became the dominant land animals.