Read the passage and choose the best answer.

Instagram was founded by Kevin Systrom and Mike Krieger in October 2010. Systrom and Krieger initially wanted to create an application for mobile photography called Burbn, but upon developing their idea further, they found that it was too similar to the existing search-result app called Foursquare. They tweaked their original idea until they came up with a photo-sharing app. The name “Instagram” is a combination of “instant camera” and “telegram.”

From the outset, Instagram proved extremely popular. Only two months after its launch, it achieved a million users and reached ten million users in its first year. The simple idea of sharing photos in a social media setting appealed to a wide variety of phone users. As time went on, Systrom and Krieger began making a series of technology-related improvements to the app —making it compatible with Android and Windows phones, for example - as well as improving the user experience. In January 2011, it added hashtags, offering users the ability to find posts and people related to common interests. As Instagram grew into one of the most popular apps in the world, tech titans took notice. In 2012, Facebook purchased Instagram for one billion dollars.

In November 2012, Instagram launched web versions of user profiles, giving desktop users the ability to access Instagram profiles. However, the website profile launch retained limited functionality and lacked a search bar; the feature was redesigned in 2015. Instagram also began allowing the upload of non-square photos to the app in August 2015, a notable shift from the look and feel of the app since its inception. Rather than cropping down larger photos to a neat square, users could upload any photo of any dimension to share with friends and followers.

In March 2016, Instagram changed the nature of its news feed, the place where users scroll through newly-posted photos from those they follow, from chronological to algorithmic. “Algorithmic” means that Instagram uses computer algorithms and artificial intelligence to make “decisions” on what its data predicts you’ll like best. While this decision was met with backlash at first, it was made in order to prevent users from missing important posts from friends and family that might have gone unnoticed with a standard chronological timeline approach. Later in 2016, the app underwent major aesthetic changes; the app itself revamped to a black-and-white theme, while the app icon changed to a whimsical rainbow-colored design.

Today, Instagram boasts 800 million users. Every day, 55 million photos are uploaded and 1.2 billion likes are recorded.

Why are hashtag (#) useful on Instagram?