Answer: New bacterial cells can only arise from preexisting bacterial cells.
Explanation:
Option A is wrong because when heat was applied, there was no new bacterial growth. Most likely because the heat killed the bacteria cells. Option C is also wrong as well the third trial had nutrients but no new bacteria cells grew.
Option D is wrong because in Trial 1, there were nutrients and yet no new cells were formed. This means that growth of new cells depends on more than nutrients alone.
This leaves option B as the correct answer which is proven by the lack of growth of new cells when there were no pre-existing ones in trial 3.