In short time, I found a solution to rip DVD. The app is an open source project: HandBrake. I downloaded the app for Mac. I had to allow any app for temporary from System Preference:Security so that the app could be opened.
I tried HandBrake and it did the job as my expectation, ripped DVD to m4p movie file. Then I used Quicktime Trim feature to cut pieces we need to finish our work.