The ........... function is used to read a single character from a file.

Option A: fgetc()
This function in PHP is used to read a single character from a file. It retrieves the next character from the file pointer and advances the file pointer position to the next character.

Option B: fgets()
The fgets() function is used to read a line from a file. It retrieves a line of text from the file pointer, including the newline character at the end of the line.

Option C: fget()
There is no fget() function in PHP related to file reading. This option is incorrect.

Option D: fgetf()
There is no fgetf() function in PHP related to file reading. This option is incorrect.

Conclusion:
The function used to read a single character from a file in PHP is fgetc() (Option A). This function is specifically designed to fetch individual characters from the file, making it the correct answer to the question.