Identifying Where Bricks Are Not Used

The question asks to identify the scenario among the given options where bricks are not used.

Let's look at each option:

• Making Khoa: Khoa is a dairy product. While traditional methods of making Khoa might involve using a stove or oven built with bricks, the bricks are part of the heating structure, not the ingredients or the product itself. So, bricks are used in the process infrastructure, but not directly in the Khoa.

• Construction of plastic wall: A plastic wall is constructed using plastic materials. By definition, bricks (which are made of clay or other materials) are not used as the primary building block for a wall explicitly stated to be 'plastic'.

• Construction of walls: Bricks are one of the most common and traditional materials used for constructing walls in buildings and other structures.

• Construction of floors: Bricks can also be used for constructing floors, especially in patios, garden paths, or certain types of interior flooring.

Considering the typical uses of bricks, they are fundamental for building walls and floors. While they might be part of the setup for making Khoa in some traditional ways, a "plastic wall" is specifically defined by being made of plastic, not bricks.

Therefore, bricks are not used in the construction of a plastic wall.