Under a light microscope, a stained cell shows chromosomes lined up along the middle. what will happen next?
spindles will form and centrioles will move to opposite poles.
a nuclear membrane will form around each set of chromosomes.
chromosomes will separate and move to opposite poles

Option A, Spindles will form and centrioles will move to opposite poles.

Explanation:

The stage of cell division being described in this instance in the "Metaphase". In this phase of cell division, all the chromosomes are captured by the spindle fiber and arranged linearly along the middle of the cell.

This is the stage just before the cell division, where chromosome align themselves along the meta phase (a fictional center line) and then the two kinetochores of each chromosome get attached to the microtubules on the two opposite spindle poles.

Hence, option A is correct