Which of the following is an example of an externality? a. a flu shot that prevents a student from transmitting the virus to her roommate. b. John smoking cigarettes affecting his own health. c. my...

a.

a flu shot that prevents a student from transmitting the virus to her roommate.

b.

John smoking cigarettes affecting his own health.

c.

my beautiful flower garden that increases the value of my property.

d.

all of the above are correct.