Introduction:
In this modern era of technology, various modes of communication are available to connect with people around the world. Each mode has its own advantages and disadvantages, including cost. Among the given options, the cheapest mode of communication is letter.

Reasoning:
To understand why a letter is the cheapest mode of communication, let's analyze the other options:

1. SMS:
SMS (Short Message Service) is a text messaging service that allows users to send short messages from one mobile device to another. While SMS is convenient and widely used, it typically incurs a cost per message. Depending on the country and service provider, this cost can vary. Therefore, SMS is not the cheapest mode of communication.

2. Mobile Phone:
Mobile phones are widely used for communication, providing various means such as voice calls, video calls, and messaging apps. While mobile phones offer convenience and instant communication, they require a mobile plan or prepaid credits to make calls or send messages. This makes mobile phones a relatively more expensive option compared to a letter.

3. Email:
Email is a popular mode of communication for sending messages and files electronically. It is cost-effective for long-distance communication as it does not incur additional charges for sending messages. However, to access email services, one needs an internet connection and a device such as a computer or smartphone. These requirements make email relatively more expensive compared to a letter.

Why is a letter the cheapest mode of communication?
A letter, on the other hand, only requires a piece of paper, an envelope, and a stamp for postage. These costs are minimal and can be easily afforded. Additionally, a letter can be sent to any location without the need for an internet connection or a mobile phone. The cost of sending a letter is fixed regardless of the distance, making it a cost-effective option for communication.

Conclusion:
Considering the cost of various modes of communication, it is evident that a letter is the cheapest option. While other modes like SMS, mobile phones, and email are convenient and widely used, they involve additional costs for communication. Therefore, for individuals seeking a budget-friendly mode of communication, sending a letter remains the most economical choice.

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