Answer:
The correct answer would be she has probably already had all the strains of colds and viruses in her office.
Previous exposures to the strains of colds and viruses helped Andrea to develop adaptive immunity in her body.
Adaptive immunity helps in developing the memory against specific pathogens and thus helps in providing long-lasting protection against recurrent infections.
For example, after vaccination against a specific pathogen, our body becomes immune against that particular pathogen.