is my reasoning for enantiomers/meso compounds correct?

[![enter image description here](https://i.stack.imgur.com/K7KFk.png)](https://i.stack.imgur.com/K7KFk.png)


I think a and b are enantiomers because a has R configuration but b has S configuration. 


I think c and d are identical compounds which makes them a meso compound. If you just turn it 180 degrees they look the same to me. Am I right or is there something wrong with what I'm saying?


