The appearance P : this dinosaurs were at their peak Q : of the first mammals on the earth R : at the time when S : went almost unnoticed The Proper sequence should be:

The correct answer is: D. RPQS

The appearance of the first mammals on Earth went almost unnoticed at the time when dinosaurs were at their peak.

• R – The first mammals appeared on Earth.
• P – Dinosaurs were at their peak.
• Q – The appearance of the first mammals went almost unnoticed.
• S – This happened at the time when dinosaurs were at their peak.

The other options are incorrect because they do not follow the correct sequence of events. For example, in option A, the appearance of the first mammals is said to have happened before dinosaurs were at their peak. This is not possible, as the first mammals appeared after dinosaurs.