The correct answer is B. Tea and coffee.
Substitutes are goods that can be used in place of each other. For example, tea and coffee are both beverages that can be consumed to quench thirst. If the price of tea increases, consumers may switch to coffee, and vice versa.
A. Tea and sugar are not substitutes. Tea is a beverage, while sugar is a sweetener. Consumers do not typically consume tea and sugar together, and they do not have a similar purpose.
C. Pen and ink are not substitutes. Pens and ink are both writing instruments, but they are not interchangeable. Pens require ink to write, but ink cannot be used to write without a pen.
D. Shirt and trousers are not substitutes. Shirts and trousers are both articles of clothing, but they are not interchangeable. Shirts are typically worn on the upper body, while trousers are typically worn on the lower body.