Consider a $1\mathrm{.}00-$kg sample of natural uranium composed primarily of $238$U$,$ a smaller amount $(0\mathrm{.}720\%$ by mass$)$ of $235$U$,$ and a trace $(0\mathrm{.}00500\%)$ of $234$U$,$ which has a half$-$life of $2\mathrm{.}44105$ yr$.($a$)$ Find the activity in curies due to each of the isotopes. $($b$)$ What fraction of the total activity is due to each isotope? $($c$)$ Explain whether the activity of this sample is dangerous.