【正确答案】Topic: In our modern world, cell phones have become important for businesses.
Reason 1: One reason cell phones are so important is that the modern client typically owns a phone himself, so he will assume that others have one as well. If a modern businessman expects to develop business, he must be available at all hours, ready to take any call.
Reason 2: Another factor is that cell phones can be used to do a lot of things such as writing reports, checking statistics, sending and receiving emails, inputting vital information, and keeping communication with clients. Without cell phones, the modern business model would likely fall apart.

【答案解析】Alternative Wording(替换表达)
Synonyms (a)assume—take something for granted
(b)fall apart—descend into chaos
Paraphrases In today's world, there's no escaping the cell phone.