Which input type would allow a reader to select several options from a list of possibilities?

The correct answer is B. checkbox.

A checkbox input type allows a reader to select several options from a list of possibilities. Each checkbox represents an individual option, and the reader can select multiple checkboxes to indicate their choices. This is commonly used when there are multiple options available, and the reader can select one or more of them.

On the other hand:

• A radio input type (option A) allows the reader to select only one option from a list.
• A multi-line textbox (option C) is used for capturing longer text or multiple lines of input, but it doesn't provide a list of selectable options.
• The term "form" (option D) refers to a collection of input elements, which can include checkboxes, radio buttons, textboxes, and other input types, but it is not an input type itself.