The correct answer is B) to prevent damage to the meter movement from heat generated by the internal shunt. Ammeters measure current by shunting a portion of the current through the meter movement. This shunt can generate significant heat, which can damage the delicate meter movement if the shunt is inside the meter. By using an external shunt, the heat is generated externally, away from the meter, preventing damage to the instrument. The other answer choices are incorrect because they do not address the primary reason for using an external shunt, which is to protect the meter from heat-related damage.