Let $x$ and $y$ be optimal solutions of a Linear Programming $(LP)$ problem. Then,which of the following is true?

• A
  $z=\lambda x+(1-\lambda) y, \lambda \in R$ is also an optimal solution.
• B
  $z=\lambda x+(1-\lambda) y, 0 \leq \lambda \leq 1$ is also an optimal solution.
• C
  $z=\lambda x+(1+\lambda) y, 0 \leq \lambda \leq 1$ is also an optimal solution.
• D
  $z=\lambda x+(1+\lambda) y, \lambda \in R$ is also an optimal solution.