How many polynucleotide chains is $RNA$ composed of?

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 structure of $RNA$ resembles a cloverleaf?

The most abundant $RNA$ in a cell is......

The sequence of nucleotides $AUGCUUCUC$ indicates that it is a segment of

The most abundant $RNA$ found in a cell is .......