Antoine wants to convert millimeters into kilometers. Which operation should he choose?

One kilometer equals 1,000 meters, and each meter equals 1,000 millimeters, so 1 kilometer equals 1,000,000 millimeters. To convert a number of millimeters to kilometers, divide by 1,000,000. Therefore, Antoine should divide millimeters by 1,000,000, which is choice D.

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