What\'s the best way to copy a file from within a piece of PHP?

• A. Open the input and output files, and use read() and write() to copy the data block by block until read() returns a zero
• B. Print out a message asking your user to "telnet" in to the server and copy the file for you
• C. Use "exec" to run an operating system command such as cp (Unix, Linux) or copy (Windows)
• D. Use the built in copy() function