Why was it important to allow all the investigation materials to assume room temperature before beginning the experiment?

The temperature is kept at room temperature and mostly preferred to be constant, so that the temperature does't be a variable factor effecting the accuracy of experiment.

Temperature is kept constant to take it as a control factor, so that experimental results are not effected by such outside factors. Such control variables are important in experiments as they minimize the influences from outside.  

c.more precipitation,but only when emission levels.

the last one: artificial selection/genetic engineering

plant breeding is modifying the genetic composition of the plant - but this isn't cloning (which is specifically introducing a gene into a genome). but you are artificially selecting for the phenotype that you want.

the second one is literally genetic engineering - the gene would have been cloned first and then inserted or genetically engineered into the new plant cell (the cotton).