oninatbeforeunderaboveamongintoto连词是连接单词、短语或句子的一种词。连词不能独立担当任何句子成分，而只起连接作用。and 和，表并列和对称。I like football and table tennis.or 或者，表示选择Do you come to school by bike or by bus?or 否则，表示转折Hurry up,or you will be late.but 但是，表示转折 The bag is nice,but its too expensive.so 所以，表示原因My mother is waiting for me,so I must be off now.because 因为，表示原因He was sad because he lost his football match.