I have just found the book ... I don't understand the assignment ... the professor gave us last Monday

77. I have just found the book ____.
A. you were looking for B. which you were looking
C. for that you were looking D. you were looking
78. I don't understand the assignment ____ the professor gave us last Monday.
A. which B. that C. Ø D. All are correct
79. Students ____ get below-average exam results do not have the best prospects.
A. whose B. who C. Ø D. All are correct
80. I live in a dormitory ____ residents come from many countries.
A. where B. which C. in where D. whose