Samantha believes that flowering plants produce more flowers when they are given fertilizer. She designs an experiment in which three rose bushes are each given 100 grams of a different type of fertilizer. She observes the plants for four weeks and records the number of roses each bush produces. What element of experimental design is missing from Samantha’s experiment? *

I think she should try the experiment one set with fertilizer, and one without. The negative control group would be the set of rose bushes grown without the fertilizer, but under the exact same conditions as the experimental group. Then, if a difference is seen you can be sure it's accurate, since you tested with and without fertilizer under the same conditions. Sorry if i am wrong, I am not completly sure about this one. Again I might be wrong so sorry in advance.