For the M-O (Parent Mandatory,child Optional)case,what Action(s)should Be Taken to Ensure

Multiple Choice

For the M-O (parent mandatory,child optional) case,what action(s) should be taken to ensure minimum cardinality is maintained?

A) Define referential integrity constraint from child to parent
B) Make foreign key NOT NULL
C) Will require trigger or other application code
D) Both A and B are correct