Q. A 72 year-old woman presents with sudden weakness on the right side of the body and sensory disturbance. Neurological exam reveals: - right side weakness, - right-side loss of vibration/proprioception sensation, - and left -side loss of pain/temperature sensation. - reflexes are absent on the right side at the level of the lesion and normal on the left. Note that the reflexes are brisk below the level of the lesion on the right. Which of the following is the most likely diagnosis?