Answer:
D. All of the above
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There are three forces acting on the book. 
1. Force due to gravity
2. Force exerted downward by the hamster
3. Normal Force in reaction to the downward forces
Since the book is not moving, the net force is zero. The summation of all forces must be zero. Then we could find the normal force which is unknown (denoted as x).
∑F = -(4 kg)(9.81 m/s2) - 3 N + x =0
∑F = -39.24 N - 3N + x =0
x = 42 N
Therefore, the normal force is 42 N.
        
             
        
        
        
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit. Its basic function is to interrupt current flow after a fault is detected.
I hope that this answer helps you
        
             
        
        
        
<span>As the gases go higher in the atmosphere they start to compose or join together</span>
        
             
        
        
        
13 is the mode because it is the number that appears most often
:)