The half-life of the radioactive isotope silver-104 is 30 minutes. After how many minutes will about 20 grams of a 40-gram sample of the silver-104 isotope remain? Select one:
a. 0
b. 60
c. 90
d. 30

Harry lives in a city, and he has a lung condition known as asthma. on certain days, harry has to stay inside because pollutants in the air make it difficult for him to breathe. which of these pollution sources are nonpoint sources that might bother harry if he goes outside? choose the two that apply.