Solution: C. Pangea
The hypothesis of Continental drift suggests that in past, there was only one landmass on the Earth -Pangaea which drifted apart due to movement of plate tectonics causing earthquake. This hypothesis is supported by many evidences which includes presence of similar fossils on different landmasses, common land features such as widespread presence of glacial sediments etc.
Explanation:
The nucleus of an atom can be modeled as several protons and neutrons closely packed together.
Mass of the particle, 
Radius of the particle, 
(a) The density of the nucleus of an atom is given by mass per unit area of the particle. Mathematically, it is given by :
, V is the volume of the particle
So, the density of the nucleus of an atom is 
.
(b) Density of iron, 
Taking ratio of the density of nucleus of an atom and the density of iron as :
So, the density of the nucleus of an atom is 
times greater than the density of iron. Hence, this is the required solution.
Answer
Doggy beds and pillows haven't always been around, so wild dogs had to pat down tall grass and underbrush to make a comfortable bed for themselves and their pups. The easiest way to prepare that night's sleeping area was by walking around in a circle. The rounding ritual may also have served as a safety precaution.
