Answer: a. rise, the supply of bread to decrease, and the demand for potatoes to increase.
Explanation:
According to the Economic law of SUPPLY AND DEMAND, less supply means HIGHER prices simply because the good is becoming scarce not unlike fuel during global oil shortages.
Now, we are told that the drought reduced the supply for wheat which means the SUPPLY of wheat has DECREASED and this will translate to the SUPPLY of Bread DECREASING as well. According to the aforementioned law, prices of Bread will therefore RISE.
Since Bread prices have risen, people will seek alternatives to bread as they may not want to pay the high price. This will lead them to choosing the alternative to bread which in this case are Potatoes which would therefore INCREASE the DEMAND for potatoes.