HELP...Learning SQL

Here's the scenario:
Each student is supposed to turn in 5 assignments(1 thru' 5 "assn_num"s) I have to create a report showing a list of "assn_num" missing for all the students who have not turned in all five assignments.

Any help/hint/suggestion will be greatly appreciated!

The data looks like this :

    CLASS STUDENT ASSN_NUM ASSN_GRADE --------- --------- --------- ----------

      300      1010         1         90
      300      1010         2         97
      300      1010         3         85
      300      1010         5        100
      300      1020         1         90
      300      1020         2         97
      300      1020         3         85
      300      1020         4         90
      300      1020         5        100
      300      1030         1         90
      300      1030         2         97
      300      1030         3         85
      300      1030         4         88
      300      1030         5        100
      300      1040         1         90
      300      1040         3         85
      300      1040         5        100
      300      1050         1         90
      300      1050         2         97
      300      1050         3         85
      300      1050         4         77
      300      1050         5        100
      300      1000         1         90
      300      1000         2         97
      300      1000         5        100
      400      1020         1         90
      400      1020         2         95
      400      1020         3         98
      400      1040         1         88
      400      1040         2         90
      400      1040         3          0
      400      1050         1        100
      400      1050         2         91
      400      1050         3         88