Which of the following expresses the temperature T(t) of a cooling body at time t in terms of its ambient temperature Ts, initial temperature T0, and cooling constant k?
a) T(t)=Ts+(T0−Ts)ekt
b) T(t)=Ts+T0e−kt
c) T(t)=Ts+(T0−Ts)e−kt
d) T(t)=T0e−kt