請依下文回答第 21 題至第 25 題
        There is an app for everything these days. You have a mobile app for waking you up in the morning to one that lets you play music from your favorite play store, read the news and watch the latest TV serials. But what is it that makes an app truly great and keep users from removing it from their devices later on? The   21      for developers who create these apps is pretty fierce. Studies show an app that doesn't keep users interested would be   22   within the first three days. It is important to understand that people share things which evoke positive emotion or provide them with good experiences. A mobile app that offers value is also likely to be recommended by a friend or acquaintance more. If you want your app to be shared a lot after   23   , ask yourself some questions: Does your app offer something your target audience will like? Does it have anything worth sharing? You also need to avoid   24    your users by giving them unnecessary features, advertisements, or untimely push notifications. Another important tip is always to test your app on real users, which can help you pinpoint annoyances and use them as a basis to improve your product. Anything from connectivity to navigation that makes users experience inconvenience in any way is a   25   . How successful your product is depends on your users. You need to look out for anything that might prompt users to abandon your app.
【題組】21
(A) communication
(B) competition
(C) cooperation
(D) consideration