The correct answer is D. All of these.
The base unit method, cost per function method, and
cost per square metre are all methods adopted for developing the approximate or conceptual estimates.The base unit method is a method of estimating the cost of a project by multiplying the number of units of each type of
work by the unit cost of each type of work. The unit cost of each type of work can be obtained from past experience or from published sources.The cost per function method is a method of estimating the cost of a project by estimating the cost of each function that the project will perform and then adding up the costs of the individual functions. The cost of each function can be estimated from past experience or from published sources.
The cost per square metre method is a method of estimating the cost of a project by multiplying the area of the project by the unit cost per square metre. The unit cost per square metre can be obtained from past experience or from published sources.
The base unit method, cost per function method, and cost per square metre are all approximate methods of estimating the cost of a project. They are not as accurate as detailed estimates, but they are faster and easier to prepare.