The correct answer is: dependent variable.
There are two main variables in an experiment: the independent and dependent variable.
The experimenter changes the independent variable and that has the influence on dependent variable. So, the effect on the dependent variable is tested (observed and recorded).
The answer would be water.
I believe the answer is The spindle fibers
Microtubule will form the spindle fibers that will grab the chromosome. The formation of microtubule will be start from prophase and it will have role in moving the chromosome through the metaphase and anaphase. If the substance disrupting the formation of microtubules, then spindle fibers will not be formed.