19、Which is true about invalid PL/SQL objects?
A) They are automatically recompiled against the new definition of a referenced object at the same time as the referenced object is modified.
B) They can be manually recompiled only by using SQL commands.
C) They are automatically recompiled against the new definition of a referenced object when they are called.
D) They must be manually recompiled before they can be used if a DDL is performed on a table that is referenced in the PL/SQL object.
Answer:D