'I wonder if the prof took attendance already.

prof＝professor，take attendance 点名。

'God， I only missed two classes and I＇m already out of it.

be out of it 是跟不上的意思，所以得 catch up with them ASAP

'Hey， I got the whole info from the upperclassman.

info＝information， upperclassman 学长，也可能学长为seniors或 older guys

'That guy is a tough nut. I guess this class is a bear！

难缠的老师称为 tough nut，bear表示很难的科目。

' I struggle for words when asked a sudden question.

struggle for words 难以回答