$A$ non-metal $X$ exists in two different forms $Y$ and $Z$. $Y$ is the hardest natural substance, whereas $Z$ is a good conductor of electricity. Identify $X$, $Y$ and $Z$.

• A
  $X = \text{Carbon}, Y = \text{Diamond}, Z = \text{Graphite}$
• B
  $X = \text{Sulfur}, Y = \text{Diamond}, Z = \text{Graphite}$
• C
  $X = \text{Carbon}, Y = \text{Graphite}, Z = \text{Diamond}$
• D
  $X = \text{Phosphorus}, Y = \text{Diamond}, Z = \text{Graphite}$