I don't understand, what is the question you're supposed to answer?
Answer: 4
Explanation:
The pairing of the third (3') base of the mRNA codon and the first (5') base of the tRNA anticodon are less constrained by base stacking.
Density is a derived unit because it's not reported as a pure unit. (A pure unit would be something like kilograms or meters.) In contrast, the units for density are kg/m3. Density is the ratio of mass to volume; mass has the unit 'kilograms' (kg) and the unit for volume is cubic meters (m3).
Density is an intensive property, which means the amount of the material is irrelevant. The density of a substance is constant.
Answer:
Because flu viruses evolve so quickly, last year's vaccine may not protect you from this year's viruses. New flu vaccines are released every year to keep up with rapidly adapting flu viruses.
