If you hear the sound of a mobile phone beeping in a bag or pocket, you could think that someone has received a text message. Text messaging, or texting, is the art of sending a short, electronic message between two mobile phones. The users should pay a certain amount to send messages via SMS--- short message service. But in the last few years, with the development of smart phones, messaging in this way has been _  The rise of smart phones has seen an increase in the use of instant messaging apps. The apps offer a cheap alternative to traditional texts. Using wireless internet connections, people can send a number of messages to their friends at a very low cost. Unlike traditional mobile texts, the users usually only have to pay to download the app once, after which each message they send is free. Instant messaging apps have become popular all over the world. Hundreds of millions of people use the apps to chat with their friends. These apps allow people to send pictures messages for free---something which previously was quite costly. Many of these apps also allow users to have access to a huge range of colourful emotions, which can help people express their emotions. The research company Informa said that almost 19 billion messages were sent per day using chat apps last year, compared with 17.6 billion SMS texts. And it expects the chat app market to grow to 50 billion per day by 2015. So does this really mean the end of communicating by texting? Pamela Clark-Dickson from Informa doesn't think so. She says that there are a large number of people who use normal mobile phones, particularly in developing countries and prefer the SMS messaging tool. For the moment, these users still find that SMS is the best messaging experience for them. What can we learn about instant messaging apps?
Normal mobile phones can be used to download the apps. The apps enjoy high popularity in developing countries. Only part of the messages sent by the apps are free of charge. It will cost the users some money for downloading the apps.
Question: If you hear the sound of a mobile phone beeping in a bag or pocket, you could think that someone has received a text message. Text messaging, or texting, is the art of sending a short, electronic message between two mobile phones. The users should pay a certain amount to send messages via SMS--- short message service. But in the last few years, with the development of smart phones, messaging in this way has been _  The rise of smart phones has seen an increase in the use of instant messaging apps. The apps offer a cheap alternative to traditional texts. Using wireless internet connections, people can send a number of messages to their friends at a very low cost. Unlike traditional mobile texts, the users usually only have to pay to download the app once, after which each message they send is free. Instant messaging apps have become popular all over the world. Hundreds of millions of people use the apps to chat with their friends. These apps allow people to send pictures messages for free---something which previously was quite costly. Many of these apps also allow users to have access to a huge range of colourful emotions, which can help people express their emotions. The research company Informa said that almost 19 billion messages were sent per day using chat apps last year, compared with 17.6 billion SMS texts. And it expects the chat app market to grow to 50 billion per day by 2015. So does this really mean the end of communicating by texting? Pamela Clark-Dickson from Informa doesn't think so. She says that there are a large number of people who use normal mobile phones, particularly in developing countries and prefer the SMS messaging tool. For the moment, these users still find that SMS is the best messaging experience for them. What can we learn about instant messaging apps?
A. Normal mobile phones can be used to download the apps.
B. The apps enjoy high popularity in developing countries.
C. Only part of the messages sent by the apps are free of charge.
D. It will cost the users some money for downloading the apps.
Answer: