6.That young man is honest , cooperative , always there when you need his help .______, he's reliable.
根据句意及介词短语的用法, 可知正确答案为B。
句意: 这个年青人诚实, 有合作精神, 总是出现在你需要帮助的时候。简言之, 他是可靠的。Or else “否则”; In short “简言之”; By the way “顺便说一下”; For one thing “一方面; 一则” 。故选B。
短语意思不清及句意不理解