80. What would have happened _____, as far as the river band?

　 A. Bob had walked farther　　 　　　　　　　　　　 B. if Bob should walk farther　　　　　　　　　　　　　　　　　　　　　

　 C. had Bob walked farther　　 　　　　　　　　　　 D. if Bob walked farther