Please note punctuation changes.

Originally Posted by
RonBee
In September, I was assigned to welcome the freshmen and help them to adapt themselves to the campus life.
In September, I was assigned to welcome the freshmen and help them adapt to campus life.

Originally Posted by
RonBee
It is not a tough and challenging job though, I have a chance to be face to face with the new students and communicate with them.
It is not a hard job, and I have a chance to meet the new students and talk to them.

Originally Posted by
RonBee
Compared with some junior and senior, they appear to be more energetic, vigorous and ambitious .The moment when I saw them really bring me back to my first year in university.
Compared to some juniors and seniors, they appear to be more energetic,vigorous and ambitious. When I first meet them it really takes me back to my first year at university.

Originally Posted by
RonBee
However, I can’t help wondering how long will their ambition and eagerness last after they come to realize the difficulties in study.
However, I can't help wondering how long their ambition and eagerness will last after they realize how difficult college is.
Am I close with that?
Also, what is a scenario plan?
~R

Originally Posted by
RonBee
Is it just a nine-day wonder?
Does "it" refer to the freshmen? If not, what?
~R

Originally Posted by
RonBee
According to my experience, the number of freshmen who have decided to further their study in graduate school is cut down to half in grade two, and the number is going to be in decline with the passing year.
According to my experience, the number of freshmen who decide to further their study in graduate school...and the number declines with each passing year.
What do you think?
~R