Answer:
this is because Steel is more difficult to magnetise and demagnetise but an iron core makes a temporary electromagnet because its lose its magnetism when the switch is open and and steel core is used to make a permanent electromagnet
A........................
A is the correct answer because paleomagnetism is the record of Earth's strength and direction in it's magnetic field. It helps us in the knowledge of evolution.
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B. The amount of sleep students received before the exam