We have to consider that nitrogenous bases are those molecules in which our genes are written. The DNA can vary between species from thousands to millions of these molecules, and we classify them also in purines (Adenine and Guanine) and pyrimidines (Cytosine, Thymine, and Uracil (present only in RNA)), both complements each other, so we cannot find purines linked to purines or pyrimidines linked to pyrimidines, but also purines linked to pyrimidines, and we can differentiate one from the other in the fact that purines have two carbon rings instead of one, like pyrimidines.
So the mRNA for a DNA fragment that has TAC-GCA-TGG, is the following:
C) AUG-CGU-ACC.