Điền liên từ but,so,however,therefore thích hợp  1.this is the shortest way to the city centre ;....it is not the only way 2.the boy was able to learn english ,....he is very lazy 3.he didn'n attend the lesson,...he could not do his homework . 4.the rice is 6000 dong per kilo,....we bought 10 kilos 5.your son is heading to the right direction;...i think you should encourage him to learn harder. 6.it is very late now,....she is still at her office . 7. It was midnight,.....they closed the restaurant and went home. 8.he had written to her many times,...she didn't give any reply,....the had been out of touch ever since