Answer:
D. All of the above.
Explanation:
Iron has a constant density, which means 2-kg block will have twice as much volume as 1-kg block; therefore, choice A is correct.
Inertia is defined by the equation F = ma: it measures how hard it is to change the motion of an object. The inertia of the the 1-kg solid iron is
F = 1a,
And the inertia of the 2-kg solid iron is
F = 2a,
which is twice as much that of the 1-kg block; therefore, choice B is correct.
The mass of the 2-kg block is twice as much as that of the 1-kg block; therefore, choice C is also correct.
Thus, all of the choices are correct (D).
Rain will be expected in Billings
Their combined momentum after they meet is 0 .
Let say the two train cars are of masses
and 
now if the speed of two cars are
and 
then we can say that the momentum of two cars before they collide is given by

here two cars are moving in opposite direction so we can say that the net momentum is subtraction of two cars momentum.
Now since in these two car motion there is no external force on them while they collide
So the momentum of two cars are always conserved.
hence we can say that the final momentum of two cars will be same after collision as it is before collision
