Which option correctly pairs a phase with its key event?

• A. Metaphase — Sister chromatids separate
• B. Anaphase — Chromosomes align at the center
• C. Telophase — Spindle fibers form
• D. Metaphase — Chromosomes line up in the middle of the cell

Answer: (D)

In mitosis, the defining event of metaphase is the alignment of chromosomes along the cell’s equator, or metaphase plate, with sister chromatids still held together at the centromeres and attached to spindle fibers. This makes the statement "Chromosomes line up in the middle of the cell" the correct pairing for metaphase. The other recalled events don’t match the phase: sister chromatids separate during anaphase, chromosomes align at the center during metaphase, and spindle fibers form earlier in prophase rather than in telophase.