You want to identify a selector in a Type into activity that will be used...

A selector is a string of characters (XML fragment) that identifies a UI element uniquely within the UI hierarchy. A selector must be valid for only one element in an application, otherwise the Type into activity will not be able to find the correct target for typing the text. If a selector is valid for more than one element, it is considered ambiguous and unreliable. Therefore, the answer is A. 1 element. References: Selectors, Type Into