If demand increases in a perfectly competitive market, then all of the following options will be correct. So the correct option among the given options is option C - All of these are correct. Here is a 150 word explanation of why all of these options are correct in a perfectly competitive market.When demand increases in a perfectly competitive market, the following effects take place: firms are required to increase their production to meet the rising demand, and as a result, the short-run supply curve shifts to the right. At the same time, the price in the market will be higher due to the increased demand. However, this is not sustainable as in the long run, new firms will enter the market to capture some of the profits. These new firms will cause the supply curve to shift further rightward. As a result, the price in the market will fall until it reaches the equilibrium price. Therefore, all of the given options are correct when the demand increases in a perfectly competitive market.