Which labels belong in the areas marked X and Y? X: absorbs heat
Y: involves a change between solids and liquids
O X: absorbs heat
Y: involves a change between gases and solids
O X: involves a change between solids and liquids
Y: releases heat
O X: involves a change between gases and liquids
Y: releases heat

You need to be more specific.  i really don't know what a "motion map" is.you can draw a graph of an object's position, distance, displacement, speed,velocity, or acceleration versus time, or you can draw a graph of the object's x-position versus its y-position and not give any information about time at all.if the graph presents position or displacement against time,  then constant velocity is a straight line . . i.e. a line that has  constant slope.if the graph shows speed against time, then constant velocityis a horizontal piece of line.if the graph shows acceleration against time, then constant  velocity is a piece of line that lies on the x-axis . . it's value is zero. 

Answer (d) the universe had cooled enough for atoms to combine, protons and neutrons were too far apart to form nuclei;

Hey did u get the answer?