Arrange the sentences A, B, C, and D from a logical sequence between sentences 1 and 6.
1. The history of mammals dates back at least to Triassic time.
A. Miocene and Pliocene time was marked by culmination of several groups and continued approach towards modern characters.
B. Development was retarded, however, until the sudden acceleration of evolutional change that occurred in the oldest Paleocene.
C. In the Oligocene Epoch, there was further improvement, with appearance of some new lines and extinction of others.
D. This led in Eocene time to increase in average size, larger mental capacity, and special adaptations for different modes of life.
6. The peak of the career of mammals in variety and average large size was attained in this epoch.