【正确答案】 C

【答案解析】[解析] be bound to意为“必定，一定”，符合题意，如：It's bound to rain soon. 不久一定会下雨。而obvious作“明显的，显而易见的”讲，如：It's obvious that two and two make(s) four. 2加2等于4，那是明明白白的。be indispensable to意为“必不可少的，必需的”，如：Air, food and water are indispensable to life. 空气、食物和水是维持生命所必需的。doubtless意为“确定无疑的”，如：It is doubtless that he has mistaken my intention. 他无疑误解了我的意思。