$tRNA$ is composed of about how many nucleotides?

Which of the following nitrogenous bases has a double-ring structure?

The biologically active gene synthesized by Khorana in $1979$ from $E. coli$,which codes for $tRNA$ (tyrosine),consists of:

The genes are in the form of

In the structure of a dinucleotide,between which carbons of the sugars of two consecutive nucleotides is the phosphodiester bond formed?

Who proposed that for a double-stranded $\text{DNA},$ the ratios between Adenine and Thymine and Guanine and Cytosine are constant and equal to one?