Thanks for Dr Chuck.
At first, I should say sorry to Dr Chuck, if you have seen what I comment on the former class you will know what I mean, I messed up the cute old man's name while keeping getting knowledge from him.
Secondly, this part of all five lessons bigens to solve real questions in real world, althougn it may be too simple for the problems still a little hard for us beginners. All the lesson teaches which can be used for problems, but can't teach all because of the length and ourselves patience. It's the beginning too, and we should learn more by own to walk farther.
At last, the coursera.org is so greedy to make money even its website ending with org. More and more functions are limited unless you have paid for, even you chose to give up the certification and only want to learn.At the beginning of my learning the first lesson, it limit the quiz, and now it limit the autograder.After all ,we still have access to the video, maybe it will be limited in the furture.
Knowleage should be paid, but I can't pay 10% of my monthly incoming to the uncertain future. I will continue to deal with all the limited stuff. If my life changes better, I will paid it back.