Which of the following is not a common type of fiber-optic cable?
∙ a. Single-mode step-index
∙ b. Multimode graded-index
∙ c. Single-mode graded-index
∙ d. Multimode step-index
∙ a. Single-mode step-index
∙ b. Multimode graded-index
∙ c. Single-mode graded-index
∙ d. Multimode step-index