The correct option is
B Throw away
“Cast” means to
throw (something) forcefully in a specified direction.Hence to cast away means to throw away. Hence option B is the correct answer.
“Reject” means to not approve of something, not the same meaning as throw, hence Option A is incorrect.
“Discord’ means you disagree.
“Calculate” means to determine mathematically.
“Entrust” means to assign a task to someone.