A student was attempting to make cDNA that would code for protein Y. They began with an isolated and amplified sample of the target post-transcriptional mRNA, and all the tools required to complete the task. However, at the end of the experiment the student was left with a molecule containing ribonucleotides. What most likely went wrong?

The student forgot to add DNA polymerase
The student added RNA polymerase instead of DNA polymerase
The cloning vector already transcribed the DNA
The student forgot to add reverse transcriptase

Reverse transcriptase is an enzyme, also called DNA polymerase or RNA-dependent, responsible for carrying out the transcription process, which corresponds to an “inverted copy”, as opposed to the cellular pattern. In other words, this enzyme polymerizes DNA molecules from RNA molecules, the opposite of what commonly occurs in cells.

The student, exposed in the question, wanted to create cDNA through an isolated and amplified mRNA sample, but this student did not use reverse transcriptase, so it would be impossible for his experiment to have good results.