A Message for Myoung Heon

Hello Myoung wherever you are! I thought it was very nice of you to read and respond to my English grammar post on my Write--Write--Write blog. Most people think that they have to be members of the blog to make a "COMMENT" on a post, but that is not true. ANYONE can COMMENT simply by clicking on COMMENT and typing whatever they want to say.
Now, with regard to your comment: Your sentence was like this: The doctor,who flew to Pakistan, helped four people on the flight with medical emergencies.

It should have been like this: The doctor who flew to Pakistan helped four people on the flight with medical emergencies.------The clause "who flew to Pakistan" is essential to the meaning of the sentence and therefore would not be set off with commas.
You may notice,Myoung, that I have changed my original post to make a difficult concept a little clearer.
Myoung, if you would like to join my blog, send me an e-mail and I will send you an invitation by return mail. My e-mail address is leocoleman@rocketmail.com
Again,thank you and I hope I was of some help.