4 question plz

QUESTION 1 For the following data (blank spaces are nulls), what would be one of the valid primary keys for the table A C D 1 open 10 cat 1 closed 10 dog 4 open 10 dog 5 closed 10 8 open 20 dog a. B O b.Cand D as one key O c. A and B as one key d. A QUESTION 2 For the following data (blank spaces are nulls), what would be one of the valid primary keys for the table A B C D 2 open 50 cat 4 open 40 dog 4 open 30 cow 15 open 20 5 open 10 fox a. C O b.A . O d.D QUESTION 3 For the following data (blank spaces are nulls), what would be one of the valid primary keys for the table B Ic D 1 open 11 cat 2 open 15 dog 2 closed 15 dog 2 open 20 fox O a. C. O b. D O c. B and C as one key O d. A and D as one key QUESTION 4 For the following data (blank spaces are nulls), what would be a valid foreign key in the first table referencing the second table? B Ic D 1 open 11 cat 12 open 15 dog 2 closed 15 dog 2 open 20 fox G 10 15 20 . cat dog fox E F 1 open 2 closed 2 O a. A referencing E O b.D referencing H O c. Creferencing G O d. B referencing F