The correct answer is: C. Raft footing
A raft footing is a thick reinforced concrete slab that covers the entire area of a structure to support heavy concentrated structural loads. It is also known as a mat foundation or a floating foundation. Raft footings are used in areas with poor soil conditions or where there is a risk of settlement. They are also used for large, heavy structures such as buildings and bridges.
Combined footings are used to support two or more columns that are close together. They are made up of two or more footings that are connected by a beam. Strap footings are used to support two or more columns that are not close together. They are made up of a single footing that is connected to the columns by straps.
Option A is incorrect because a combined footing is used to support two or more columns that are close together. Option B is incorrect because a strap footing is used to support two or more columns that are not close together. Option D is incorrect because it is not a valid option.