Stereochemistry and stereoisomers

See Morrison and Boyd Chapter 4, §4.2 where a number of possible structures for methane are discussed. The correct shape can be derived from the number of isomers, in particular disubstituted compounds, of the type CH2XY.
The structures from Problem 4.2 will be shown, which will help you to answer the question: are the structures in each row completely different? mirror images? superimposable (=identical)?

a. The flat rectangle structure


A B C
Question: Hopefully it is clear that C differs from A and B, however, what is the relation between A and B?

A and B are:

identical
mirror images
completely different

Continue with the flat, square structure,

the pyramidal structure,

and the tetrahedral structure.

Next subject: enantiomers.