Two things have to be keep in
 mind:
 
 1.When we say turn off all other
 independent sources:
 ØIndependent voltage
 sources are replaced by 0 V (short circuit) and 
 ØIndependent current
 sources are replaced by 0 A (open circuit). 
 2.
 2.Dependent sources are left intact because they are controlled by circuit
 variables.