Which method is used to obtain a pure sample of copper(II) sulfate crystals?
- AAdd an excess of copper(II) carbonate to dilute sulfuric acid, filter and evaporate the filtrate until crystals start to appear.
- BAdd an excess of copper(II) carbonate to dilute sulfuric acid, filter off the remaining solid and dry it in an oven at $100^\circ\text{C}$.
- CWarm an excess of copper(II) oxide with dilute sulfuric acid and evaporate the mixture to dryness.
- DWarm an excess of copper(II) oxide with dilute sulfuric acid and filter off the crystals formed.