The principle of resistance training that suggests that muscles should be gradually required to do more than they are used to doing is
a. duration.
b. tension.
c. specificity.
d. overload.

The principle of resistance training that suggests that muscles should be gradually required to do more than they are used to doing is D. OVERLOAD.

The principle of overload states that a greater than normal stress or load on the body is required for training adaptation to take place.

Overload refers to the amount of load or resistance, providing a greater stress, or load, on the body than it is normally accustomed to in order to increase fitness.

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.