The correct answer is: A. Activity of an excavation of a footing.
The network of a project represents the activities that need to be completed in order to finish the project. The activities are represented by arrows, and the events are represented by circles. The arrows show the order in which the activities need to be completed. The events show the points in time when the activities are completed.
In the given figure, the activity of excavation of a footing is represented by the arrow from event No. 1 to event No. 2. The activity starts at event No. 1 and ends at event No. 2. The activity takes 8 units of time.
Option B is incorrect because the activity of excavation of a footing does not start at event No. 1 and end at event No. 2. The activity starts at event No. 1 and ends at event No. 2.
Option C is incorrect because the activity of excavation of a footing does not take 8 units of time. The activity takes 8 units of time.
Option D is incorrect because the activity of excavation of a footing is represented in the network of the project.