A sample of radioactive material has a half-life of $20$ minutes. Which statement is correct?
- AAfter $30$ minutes, less than half of the material has decayed.
- BAfter $40$ minutes, all of the radioactive material has decayed.
- CAfter $60$ minutes, an eighth of the radioactive material remains.
- DAfter $120$ minutes, a sixth of the radioactive material remains.