While testing patients for the RNA virus COVID$-19,$ two coworkers are coming to you for advice. They have performed a polymerase chain reaction $($PCR$)$ experiment just after RNA extraction. The PCR reaction was run with a buffer mix containing specific DNA primers, nucleotides, Mg$2+,$ heat$-$resistant DNA polymerase and RNA extracted from COVID$-19$ virus. To the surprise of your coworkers, their experiment failed. What is the mistake that your coworkers made? $($Several options may be selected$)$

Question $55$ options:

Mg$2+$ is an inhibitor of DNA polymerase.

The heat resistant DNA polymerase is not appropriate. Using E$.$ coli prokaryotic DNA polymerase will provide a more accurate result.

They used RNA extracted from COVID$-19,$ in place of using reverse$-$transcribed RNA or cDNA.

COVID$-19$ cannot be studied by this approach.

They used DNA primers, while they should use RNA primer.