Below are two statements,one labeled as Assertion $(A)$ and the other as Reason $(R):$
Assertion $(A)$: Among group $13$ elements,boron's melting point is unusually high $(2453 \ K)$.
Reason $(R):$ Solid boron has a strong crystalline lattice.
In the context of the above statements,choose the correct answer from the following options:

• A
  Both $A$ and $R$ are true,but $R$ is not the correct explanation of $A.$
• B
  Both $A$ and $R$ are true,but $R$ is the correct explanation of $A.$
• C
  $A$ is true,but $R$ is false.
• D
  $A$ is false,but $R$ is true.