Which of the statements are correct?

where (B) and (C) are:

Enantiomers if $\mathrm{R}\ne {\mathrm{R}}^{\mathrm{\prime }}\text{. }$.

Diastereomers if $\mathrm{R}\ne {\mathrm{R}}^{\mathrm{\prime }}\text{. }$

Both are meso and hence the same compound if R = R'.

An equimolar mixture of (B) and (C) is a racemic mixture if $\mathrm{R}\ne {\mathrm{R}}^{\mathrm{\prime }}\text{. }$