Explanation:

Introduction:
In this question, we are given four options: Internet, Newspaper, Letter, and Radio. We have to identify the option that cannot be grouped with the other three in terms of communication.

Grouping the Options:
To group the options, we need to understand the similarities and differences among them.

Internet:
- The internet is a global network of computers that allows people to communicate and share information.
- It provides various means of communication such as email, messaging apps, video calls, social media platforms, etc.
- It is a modern form of communication and is widely used across the globe.

Newspaper:
- A newspaper is a printed publication containing news, articles, and advertisements.
- It is a traditional form of communication and provides information to a large number of people.
- It is typically published daily or weekly and is delivered to people's homes or available at newsstands.

Letter:
- A letter is a written or printed message that is sent from one person to another.
- It is a personal form of communication and is often used for formal or informal purposes.
- It is typically sent through postal mail and can be handwritten or typed.

Radio:
- Radio is a wireless communication technology that allows the transmission of audio signals through electromagnetic waves.
- It is a broadcast medium where radio stations transmit programs that can be heard by people with radio receivers.
- It is a mass communication medium and provides entertainment, news, music, and other content.

Identifying the Option:
From the above analysis, we can see that all the options - Internet, Newspaper, and Radio - are forms of mass communication that reach a large number of people. However, the option 'Letter' is a personal form of communication that is sent from one person to another. It is different from the other three options as it does not involve mass distribution or broadcasting.

Conclusion:
Therefore, the option 'Letter' cannot be grouped with the other three options - Internet, Newspaper, and Radio - as it is a personal form of communication rather than a mass communication medium.