Answer:
The correct answer is C.
Step-by-step explanation:
To pick up four clips at the tip of the nail, wrap the wire around the nail more times than it already has. This is because the attraction force of the electromagnet is directly proportional to the square of the magnetic field that is generated by passing a current through the coiled wire. The magnetic field, in turn, is proportional to the number of turns that this wire has around the magnetic element, so it is necessary to increase the number of turns so that the strength of the electromagnet is greater.
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