11.Three hundred students entered the swimming competition last year. A.Three hundred students take part in the swimming competition last year. B.Three hundred students took part the swimming competition last year. C.Three hundred students took part in the swimming competition last year. D.Three hundred students took part at the swimming competition last year. 12.The weather was terrible. We had a good time. A.Even though the terrible weather, we had a good time. B.Although the weather was terrible, we had a good time. C.The weather was terrible; moreover,we had a good time. D.Because the weather was terrible, we had a good time. 13.You need to work harder; otherwise, you won't get a passing grade. A.Although you need to work harder, you won't get a passing grade. B.Unless you work harder, you won't get a passing grade. C.If you work harder, you won't get a passing grade. D.You need to work harder, yet you won't get a passing grade. (Giải chi tiết giúp ạ !)