Which is the best practice when dealing with formulas and functions in EXCEL?

Which of the following is a way the operating system prevents unknown or unauthorized users from accessing the system?

You are almost finished updating a web site. as part of the update, you have converted all pages from html 4.0 to html5. the project is currently on schedule. however, your project manager has been asked by the marketing team manager to justify a day of time spent validating the site's html5 pages. the marketing team manager does not have technical knowledge of the internet or the web. which is the most appropriate explanation to provide to the marketing team manager?

Which location-sharing service offers items for users as a gaming component and also allows them to collectively link their check-ins to publish a trip? a. whrrl b. buzzd c. foursquare (this option is wrong i already tried) d. gowalla for plato