Why is having an extra chromosome 21 tolerable to the point that someone with this condition can survive to maturity?

I think that having an extra chromosome 21 is tolerable to the point that someone with this condition can survive to maturity because it does not replicate.

There should only be a pair of chromosome 21. In the event that there are 3 chromosome 21, the person that has this extra chromosome has Down syndrome. Changes in the number and structure of this chromosome may result to delayed development, intellectual disability, but not immediate death.

This bacteria must be very strong as it has a large amount on antibiotic targeting it. this bacteria could be one of many different types and it is very hard to tell which one with out more information.

Need the answers if its a multiple choice question