A.I. Explanation:

Option 1: "The chromosome duplicates to form chromatids."

Explanation: The text clearly states that in prophase, "each chromosome duplicates to form two sister chromatids." This directly supports the correct answer, as it describes the process occurring in prophase accurately. The use of the term 'duplicates' indicates that the chromosomes are actively preparing for division, which aligns with the main idea of mitosis as a process of cell division.

Option 2: "The chromosome duplicates to form centromeres."

Explanation: This option is incorrect because the text does not mention that chromosomes duplicate to form centromeres. Instead, it specifies that chromosomes duplicate to form sister chromatids. Centromeres are parts of the chromosomes that hold the sister chromatids together, but they are not formed from the duplication process.

Option 3: "The chromosomes become inactive."

Explanation: This option is incorrect as the text does not suggest that chromosomes become inactive during prophase. In fact, the opposite is true; the chromosomes are actively duplicating and preparing for division, which contradicts the idea of them becoming inactive.

Option 4: "The chromosomes expand."

Explanation: This option is incorrect because the text does not mention that chromosomes expand during prophase. The focus is on the duplication of chromosomes into sister chromatids, not on any expansion. Therefore, this option does not accurately reflect the information provided in the text.