The correct answer is A. Concrete cured.
An event is a specific occurrence that happens at a particular time and place. It is a happening or occasion that takes place.
Concrete curing is a process that occurs when concrete is exposed to water. This process causes the concrete to harden and become stronger. It is a chemical reaction that takes place between the cement and water in the concrete.
Fixing of door is a process of installing a door in a frame. It involves measuring the door, cutting the frame to size, and installing the door in the frame.
Plastering of walls is a process of applying a layer of plaster to the walls of a building. It is done to create a smooth and finished surface.
Selecting sites is a process of choosing a location for a building or other structure. It involves considering factors such as the availability of land, the cost of land, and the zoning regulations.
Out of these options, only concrete curing is an event. The other options are processes.