Final answer:
There is insufficient information to determine when the fish will start to get sick as the volume of the water and the critical threshold for the fish's wellbeing are not provided in the question.
Step-by-step explanation:
To determine how many minutes it will take before the fish start to get sick when the drain opens and water is drained at a rate of 20 liters per minute, we need more information regarding the volume of the fish's habitat or the point at which the water level becomes too low for the fish's safety.
Without specific details on the volume of the water or the critical threshold for the fish's wellbeing, we cannot accurately calculate the exact time until the fish begin to get sick. The values provided in the question seem to be options for a different scenario that are unrelated since they refer to the volume of a pool and water flow rates rather than the fish tank scenario described.