Answer
The correct answer is:
B. Between 2 units and 8 units
Work Step by Step
If destructive interference occurs, then the amplitude will be $5~units - 3~units$ which is $2~units$
If constructive interference occurs, then the amplitude will be $5~units + 3~units$ which is $8~units$
Since these two values are the extreme points, the range of possible amplitudes is $2~units$ to $8~units$
The correct answer is:
B. Between 2 units and 8 units
