Which of the following would be the best way to test your server for its weaknesses if you are planning on hosting an eCommerce Web server and you are intent on making the server secure against all external attacks possible?
DDoS is only one potential type of attack, if you must choose only one option making sure you've properly patched your server is the best answer, vulnerability testing should also be done but that was not given as an option.
Ping the server will only ensure if the connectivity is proper. Simulating a DoS attack could only test for a very few vulnerabilities on the server. DDoS (Distributed DoS) would test for more vulnerabilities on the server than the DoS would. Checking for patches and antivirus is just a precaution. It is not a process of testing for vulnerabilities.