How many polynucleotide chains are present in the structure of $RNA$?

Write a short note on the $RNA$ World.

Dominance of $RNA$ world is proved by

What is the $3D$ structure of a transfer $RNA$ $(tRNA)$ molecule?

How many main types of $RNA$ are there?

Which of the following statements is false for $RNA$?
$(i)$ $RNA$ can directly code for the synthesis of proteins
$(ii)$ It is a very common process to synthesize $DNA$ from $RNA$
$(iii)$ $RNA$ is used as genetic material only in humans
$(iv)$ One polynucleotide chain is present in $RNA$