Address Book is the correct answer.

Explanation:
An address book is a digital or physical record where individuals can store contact information of people they are in regular touch with. It serves as a centralized location to store and organize email addresses, phone numbers, and other relevant details of friends, family, colleagues, and acquaintances.

Here is a detailed explanation of why an address book is the most appropriate option for saving the email addresses of friends who are in regular touch:

1. Purpose of an Address Book:
- An address book is specifically designed to store contact information.
- It allows individuals to quickly access and retrieve the email addresses and other details of their contacts.

2. Contact Management:
- An address book provides a systematic way of managing contacts.
- It allows users to categorize contacts into different groups, such as friends, family, work, etc.
- This categorization enables easy searching and filtering of contacts.

3. Digital Address Books:
- With the advancement of technology, digital address books have become popular.
- Digital address books can be in the form of applications or software on computers, smartphones, or online platforms.
- These digital address books provide convenient features like search functionality, backup options, and synchronization across devices.

4. Accessibility and Convenience:
- Storing email addresses in an address book ensures easy accessibility whenever required.
- It eliminates the need to remember or search for email addresses in various places.
- Address books are often integrated with email clients, making it effortless to compose emails by simply selecting the desired contact.

5. Additional Information:
- Apart from email addresses, address books can also store other relevant information about contacts, such as phone numbers, home addresses, birthdays, and notes.
- This comprehensive information makes it easier to maintain a complete record of contacts.

In conclusion, an address book is the most suitable option for saving the email addresses of friends who are in regular touch. It provides a centralized and organized way of managing contact information, ensuring easy accessibility and efficient communication.

Where do you save the e-mail addresses of your friends who are in regular touch with you?
To save the e-mail addresses of friends who are in regular touch, you can use various methods. However, the most common and convenient way to store and manage contact information is through a digital platform or application. There are several options available for this purpose:
1. Contacts:
- The most suitable option for saving e-mail addresses is the Contacts feature available on most devices and email services.
- Contacts allow you to create a dedicated list for your friends and manage their contact details, including e-mail addresses and other relevant information.
- You can easily access and update the contact information whenever needed.
2. Phonebook:
- If you prefer to store contacts directly on your mobile device, you can utilize the phonebook feature.
- Phonebook applications on smartphones enable you to create a contact list and include e-mail addresses along with other contact details.
- This allows for easy access to your friends' e-mail addresses whenever required.
3. Address book:
- Some email services or software provide an address book feature specifically designed for managing contact information.
- You can store your friends' e-mail addresses in an address book, making it convenient to find and use their contact details when sending emails.
4. File:
- If you prefer a more manual approach, you can create a separate file on your computer or cloud storage to store your friends' e-mail addresses.
- This could be a simple text document or a spreadsheet where you list the names and corresponding e-mail addresses.
- However, managing contacts through a file may require more effort to keep it up to date compared to using dedicated contact management features.
Overall, the most efficient and user-friendly method to save and manage e-mail addresses of friends in regular touch is by utilizing the Contacts feature available on devices, email services, or dedicated address book applications. This ensures easy accessibility, organization, and maintenance of contact information.