(x-t)graph

Graph-b is correct .

 

Distance is scalar quantity. Distance will always increase with time . Distance can not be negative .

 

Distance can not decrease with time .

 

( Displacement which is vector can decrease with time or can be negative )

 

In graph-a and graph-d , distance decreases with time .

 

In graph-c , distance becomes negative for some part of time. 

 

Only in graph-b, distance increases with time . Hence only graph-b is correct.

 

Remaining graphs are not correct.