When sulfur is heated, it undergoes a \(\ldots\ldots 1 \ldots\ldots\) change as it melts. If heating continues, the sulfur then undergoes a \(\ldots\ldots 2 \ldots\ldots\) change and produces sulfur dioxide. Which words fill gaps 1 and 2?
- Achemical, chemical
- Bchemical, physical
- Cphysical, chemical
- Dphysical, physical