If necessary to design a new experiment, which of the following best explains why researchers could use measurements of intracellular lactate levels (ill) in cancer cells to assess efficacy of cancer drugs?

As we know that lactate is an essential part of glycolysis which formed by the process of fermentation. According to question cancerous cells depends on fermentation to get energy.  

By inhibiting fermentation using drug results in reduction of ILL which indicate decline on cancerous cell metabolism.

Furthermore, using cancer drug, we will see low production of lactate which means drug efficiently inhibited the energy supply to cancerous cell by inhibiting fermentation.

affects the water bodies: excessive use of fertilizers causes eutrophication. the fertilizers which are used on plants affect the quality of land on which it is used, further causing erosion of soil. the fertilizers used on plants contain harmful chemical fumes which affect the environment.

frogs. the lower the ph the higher the acid content. frogs have the highest tolerance in this scenario.