Sometimes, ___ we show our gratitude for a person is reflected in the kind of food we serve him or her．

In the US, students can do almost anything they want in class, ____ they don’t make too much noise or disturb others who want to learn from the teacher. 

The librarian promised to get the book for me ____she could remember who last borrowed it.

It is so heavy a box _____ no one can move.

Would you please tell me _____ you know is good at typing?