An electric heater rated 2.0kW is used to heat 15g of water in a kettle. The initial temperature of the water is 20°C. What time does it take to heat the water to it's boiling point.

It indicates no change in temperature and the process of matter changing its state

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. 

Ibelieve the answer is d. densityhope my answer has you : )