What are two parts to a controlled experiment

You can control time in a experiment EX: say you let a plant sit in the sun for 5 hours and then let another plant sit for an entire full 24 hours and see what's the effect well what you controlled there was the time and your dependent variable would be what ever happened to that plant.  so you can control time and you can control speed if its an object that acquires you to exert force. 

Decomposition refers to the procedure by which organic substances are dissociated into basic organic components. The procedure is a portion of the nutrient cycle and is important for reprocessing the finite substance, which holds physical space in the biosphere.

The correct answer is option D.

When the bag was harvested it comprises of oribatid mites, springtails, pseudoscorpions, predatory mesostigmatid mites, and small spiders, this clearly demonstrates the existence of predators of the scavengers. This illustrates that the litterbag is in the later phase of decomposition.