If a Class Diagram Indicates a One-To-One Relationship Between Class

Short Answer

If a class diagram indicates a one-to-one relationship between class X and class Y,then
A) there will be only one object in the system of "type" X.
B) each object of "type" X will be associated with only one object of "type" Y.
C) there will be exactly one object of "type" X and exactly one object of "type" Y.
D) an object of "type" Y cannot occur without first constructing an object of "type" X.