Which activity might to increase the validity of this experiment? 1) repeating the experiment several times 2) using two different types of euglena in each tank 3) using the same concentration of nitrate solution in each tank 4) placing the euglena tank in darkness

A should be the answer because the more you test an experiment the more data you have to rely on changing the experiment would cause you to have different outcomes making the results different and unreliable so B, C, and D is not going to be the answer Hope this helps