Final answer:
Gzfile is the function used to open a file compressed with gzip. It is pivotal in programming scenarios for reading from or writing to compressed files.
Step-by-step explanation:
The correct answer to the question is A) Gzfile. When working with files compressed with gzip, the Gzfile function is typically used to open the connection to the file. This is important in programming languages such as PHP, where you may need to read from or write to a compressed file.