True.
Windows is an operating system built by Microsoft. Chrome and Android are operating systems built by Google. MacOS (Macbook pro etc) and iOS (iPhone, iPad, Apple Watch etc) are operating systems built by Apple.
Engineers build applications or apps for all of the above operating systems (OS). For example, Microsoft Word menus will look slightly different on Windows vs on a Mac. The underlying functionality maybe the same but the way it looks may have subtle differences.
Think of the OS as the foundation of a building. Once you have the foundation, you can build a house, a skyscraper, an office building etc depending on what you want to build.
The subject line should be a brief message explaining some of the contents of the email.
They may not have enough money for the bill at the time, and its easier to pay for insurance for unseen medical procedures.
