Answer:a)Add a mobile-app extension to her ad
Step-by-step explanation: A mobile app extension is the tool that extends due to the purpose of any specific function.It creates the extension of the application's function and information towards the users. This creates a interactive environment with the user even when they are accessing other apps.
Other options are incorrect because site link will be for sharing of the link as extension,call only extension is the calling purpose and mobile website link in the ad will only be used while accessing the website. Thus the correct option is option(a).