1 – Wrong
The text does not focus on the number of people that have consumed the infected beef. It’s last sentence “so there will be two further outbreaks of vCJD, as those who consumed infected beef grow older” It’s main focus is on the future outbreaks that will occur. So this is irrelevant.
2 – Wrong
This is clearly false as those with the M-V combination do develop vCJD as they grow older.
3 – Correct
The passage assumes that inheritance of the combination of genes is more important for susceptibility rather than the M variant only. There can be two combination with the M variant: M-V and M-M. Both these combinations allow vCJD to develop. M-M develops vCJD now and M-V in the future.