What is the force that can cause two pieces of iron to attract each other?
a.
gravitational force
b.
magnetic force
c.
elastic force
d.
electrostatic force

B. Magnetic Force

Explanation:

two pieces of irons cannot attract each other unless at least one of them is magnetize. That force is called magnetism.

Is it A ?  Yes !  Two pieces of iron DO always attract each other with equal and opposite gravitational forces, although the forces are so small that we never notice them.

Is it B ?  Yes, it could be.  If at least one of the pieces of iron is magnetized, then they can attract each other with equal and opposite magnetic forces.

Is it C ?  Yes, it could be.  But the pieces of iron would have to be joined by a stretched rubber band.  Then they would attract each other with equal and opposite elastic forces.

Is it D ?  Yes, it could be.  If one of the pieces of iron carries a net electric charge, then they attract each other with equal and opposite electrostatic forces.  

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