Answer would be C, Decrease his revenue, since his output has decreased and the price remains the same.
Tom produces commemorative t-shirts in a competitive market. If he decided to decrease his output, this will decrease his revenues since his output has decreases and the price remains the same.
When there is a decrease in the quantity of a product produced by the company, the revenues will also decrease because when more quantity is sold, more revenue is generated and vice versa, keeping the price at a constant number.