Diamond and Graphite

Carbon is capable of forming many allotropes due to its valency. The above is a simplified phase diagram of carbon. Which of following explanations is correct?

a) At $25$ °C and $1$ atm, graphite is the most stable phase of carbon.

b) If we put more and more pressure on graphite while maintaining the temperature at $25$ °C, then graphite can become a diamond.

c) If we increase the temperature while maintaining the pressure below T in the diagram, then graphite sublimates into vapor.