Difference
區別
"I can always tell a graduate class from an undergraduate class," observed the instructor in one of my graduate engineering courses at California State University in Los Angeles.
“研究生班和本科生很容易就能區別開來，”在洛杉磯加利福利亞州立大學給我們研究生上工程學課的老師如此說。
"When I say, 'Good afternoon,' the undergraduates respond.
“我說‘下午好’，本科生們回答說‘下午好’。
"Good afternoon." But the graduate students just write it down."
研究生們則把我說的話記在筆記本上。”

1.tell a graduate class from an undergraduate class
tell from=tell the difference between A and B
從…可看出；通過…判斷出
eg: I could tell by his face that he was angry. 我能從他的臉上看出他生氣了。
分清…；區別…，把…與…區分開
eg: to tell the real from the false 區別真偽

2.instructor
n.指導者，教師，也有教練，輔導員等的意思。
instructor主要偏向于導師的意思。一般上課的老師都用teacher。

3.respond
不及物動詞，需加介詞to或者that引導的從句
She never responds to my letter.
He responded that he remained optimistic.

4.write it down
write down是寫下的意思。