Judge the Following Sentence According to the Criteria Given Below

Multiple Choice

Judge the following sentence according to the criteria given below. Earth's magnetic field is due to a big mass of magnetized material inside Earth because magnets function only at relatively low temperatures.

A) The assertion is correct but the reason is incorrect.
B) The assertion is incorrect but the reason is correct.
C) The assertion and the reason are both correct, and the reason is valid.
D) The assertion and the reason are both correct, but the reason is invalid.
E) Both the assertion and the reason are incorrect.