How are viruses used in gene therapy?
a. to attack the immune system
b. to carry new genes into cells
c. to infect disease-causing bacteria
d. to kill cancer cells that have "suic*de genes"

B. certain viruses are used as vectors because they can deliver the new gene by infecting the cell. the viruses are modified so they can't cause diseases when used in people.

yes, because even though a theory has a  lot of evidence to support it, it is not always true