Final answer:
RNA that could self-replicate was probably the first carrier of genetic information in primitive organisms, as supported by the RNA world hypothesis.
Step-by-step explanation:
The question regarding the first carrier of genetic information in primitive organisms is deeply rooted in the field of molecular biology and the origin of life. The consensus among many scientists today, backed by the RNA world hypothesis, is that RNA that could self-replicate (option d) was probably the first carrier of genetic information. This hypothesis is supported by RNA's ability to encode genetic instructions similar to DNA, as well as some RNAs' ability to carry out chemical reactions like proteins, thus serving both functional and informational roles in early life forms.