Samples of magnesium carbonate, $\text{MgCO}_3$, are put into crucibles R and S. The material in crucible R is heated until its mass no longer decreases, then it is left to cool. The material in crucible S is not heated. Dilute hydrochloric acid is then added to both crucibles. After the dilute hydrochloric acid is added, which observations are correct?
- AR: gas produced, S: gas produced
- BR: gas produced, S: no gas produced
- CR: no gas produced, S: gas produced
- DR: no gas produced, S: no gas produced