PhP confusion

I haven’t installed the stuff yet. I just installed MySQL on the server, and was going to install PhP, but then got this:

Malicious computer users often exploit insecurely written PHP scripts using the seven features below to gain full access to your account. Disabling these features will make it more difficult for attackers to exploit vulnerabilities in insecure scripts, but may cause applications that depend on these features to stop working.

Please check the boxes next to the features you wish have enabled. You may change your selection at any time from the edit menu after installation.
Enable ‘exec’ function
Enable ‘popen’ function
Enable ‘passthru’ function
Enable ‘proc_open’ function
Enable ‘shell_exec’ function
Enable ‘system’ function
Enable ‘allow_url_include’ feature

Can someone tell me which ones should be enabled, and which ones shouldn’t?

Merry Christmas!