What is unique about a dual-axis chart

When is an original work considered public domain? a. when posted via social media b. when it is posted on the internet c. when a copyright symbol is not included with the piece of work d. when explicit permission is given by the author / owner

How would you categorize the software that runs on mobile devices? break down these apps into at least three basic categories and give an example of each.

Which of the following is not a key player in the sale of travel products?