Need some help with SQL, possibly using group and count, or whatever it needs. Just could not find a way. Thanks a lot.

A simple table:

```
ColA   ColB
  1      A
  1      A
  2      B
  3      B
  4      C
  4      C
  5      C

```

Return all unique pairs of ColA and ColB, where for the same ColB there are more
than one distinct ColA values.  

For given data above, it shall return  

```
ColA  ColB
  2     B
  3     B
  4     C
  5     C

```