Wewentrightroundtothewestcoastby

We went right round to the west coast by __________ sea instead of driving across _________ continen

A. the … the B. / … the C. the … / D. / … /

解析：表示方式，意為“乘船”。類似詞組還有by air (乘飛機)，by land (由陸路)。第二個空缺選the，表“特指”。