Final answer:
The safest way to send and receive attachments is to use encryption. Encryption ensures that the data is protected and can only be accessed by the recipient with the decryption key. (option C)
Step-by-step explanation:
The safest way to send and receive attachments is to use encryption. Encryption is the process of converting data into a code to prevent unauthorized access. When you use encryption to send attachments, the data is protected and can only be accessed by the recipient with the decryption key.
Using a code word indicating the attachment is legitimate (option A) does not provide strong security because an attacker can still intercept the attachment and gain access to it. Only sending spreadsheet attachments (option B) does not guarantee safety as spreadsheets can still contain malicious code. Using virus scanners before opening attachments (option D) is important, but it's not foolproof as new viruses can evade detection.
Encryption is the most effective method for ensuring the safety of attachments during transmission.