The mass of a radioactive substance remaining after t days is modelled by M(t)=120e−0.08t grams. If the counting starts at the instant the measurement begins, which of the following is the most reasonable domain for the function M?
a) {t∈R∣t≤0}
b) {t∈R∣t≥0}
c) {t∈R∣0≤t≤120}
d) R