单选题 The rationale for the government"s involvement in each mode of transportation is that a strong transportation system is necessary for developing the nation"s economy or for its defense.
【正确答案】 B
【答案解析】[解析] 在给出的选项中，conviction：信念，确信；principle：原则，原理；premise：前提；tedium：方法，媒介。根据题意，只有B选项可以替换画线词语充当主语，因此答案为B。