Dinosaurs were dominant features during the period of
(A) Jurassic
(B) Cretaceous
(C) Triassic
(D) Paleocene

Hint:The dinosaurs initially appeared in the Triassic period.During this period, diverse classes of dinosaurs were observed which conquered over the planet earth.

Complete answer:
The Mesozoic era is broadly classified into three periods including Triassic period, Jurassic period and Cretaceous period. The occurrence of the first dinosaurs and mammals was noticed in the Triassic period. During the Triassic period there was a single landmass or continent and firstly the pterosaurs appeared with other dinosaurs and other animals. The dinosaurs were very dominant probably due to their large size and further they were devastated only when there were significant alterations in the environment like earthquakes, volcanic eruptions etc. Initially, the dinosaurs occurred to be smaller in size but later on Pangaea started to divide in this era. Diversification of the dinosaurs was mostly noticed in the Jurassic age and after this period, the larger sized dinosaurs were frequently observed. In the Jurassic period, both the meat-eating (carnivores) and plant-eating (herbivores) dinosaurs were nurtured vastly. Meanwhile, the continents were separating continuously and fragmented into two continents. In the Cretaceous, modern birds, ancient mammals and fishes were noticed and also the toothed birds and giant reptiles got extinct. Apart from this, the flowering plants and numerous insects developed the Cretaceous. Bulky herds of the ornithischians (herbivorous) also succeeded during the Cretaceous.

Hence the correct answer is option ‘A’.

Note: After existing over the planet Earth for about 165 million years, the Dinosaurs got extinct about 65 million years ago, probably at the last part of the Cretaceous age.