someone told me the following table isn't fit for the second database normalization. but i don't know why? i am a newbie of database design, i have read some tutorials of the 3NF. but to the 2NF and 3NF, i can't understand them well. expect someone can explain it for me. thank you,

    +------------+-----------+-------------------+
    pk                pk             row
  +------------+-----------+-------------------+
      A                  B                  C
   +------------+-----------+-------------------+
        A                  D                  C
 +------------+-----------+-------------------+
          A                  E                  C
  +------------+-----------+-------------------+