In which form of $RNA$ are most nucleotides in a modified form?

$RNA$ contains:

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

Given below are two statements:
Statement $I$: $RNA$ mutates at a faster rate.
Statement $II$: Viruses having $RNA$ genome and shorter life span mutate and evolve faster.
In the light of the above statements,choose the correct answer from the options given below:

Which form of $RNA$ is associated with the clover-leaf structure?

$RNA$ shows the following characters $EXCEPT$ . . . . . . .