A counter that measures radioactive decays from a radioactive source produces the following counts for equal time intervals of time. Time intervals (min) and counts: $0$-$10$: $424$; $10$-$20$: $395$; $20$-$30$: $413$; $30$-$40$: $363$; $40$-$50$: $366$; $50$-$60$: $294$; $60$-$70$: $301$; $70$-$80$: $253$; $80$-$90$: $212$. What conclusion can be drawn from these readings?
- Athat radioactivity is random and that the half-life is $90$ minutes
- Bthat radioactivity is random and that the half-life is uncertain
- Cthat radioactivity is spontaneous and that the half-life is $90$ minutes
- Dthat radioactivity is spontaneous and that the half-life is uncertain