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

$mRNA$ was named by:

Given below are two statements:
Statement $I$: In the $\text{RNA}$ world,$\text{RNA}$ is considered the first genetic material evolved to carry out essential life processes. $\text{RNA}$ acts as a genetic material and also as a catalyst for some important biochemical reactions in living systems. Being reactive,$\text{RNA}$ is unstable.
Statement $II$: $\text{DNA}$ evolved from $\text{RNA}$ and is a more stable genetic material. Its double helical strands being complementary,resist changes by evolving a repairing mechanism.
In the light of the above statements,choose the most appropriate answer from the options given below:

How many polynucleotide chains are present in $RNA$?

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

The smallest $RNA$ is........