Which of the following bases is present only in $R.N.A$?

Which of the following discoveries led to the term '$RNA$ world' being coined in $1980$?

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

Which of the following is a type of $RNA$?

Which of the following is not a type of $RNA$?

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 $RNA$