The correct answer is: C. both (a) and (b)
A form is a user interface element that allows users to enter data into a database or other application. It consists of a set of fields, each of which has a label and a data type. The fields are arranged in a layout, which defines where they are placed on the screen and how they are displayed. The width of each field is also defined in the layout.
Option A is correct because the layout of a form defines where data is placed on the screen. Option B is correct because the layout of a form also defines the width of each field.
Option D is incorrect because it includes option C, which is already the correct answer. Option E is incorrect because it is the opposite of the correct answer.