,18. How long _____you ____the army till now? a. did, join b. have, joined c. have, been d. have, served in我选C23. The modern technology____to shrink(缩短) the distances of runways which large and fast aircraft use.a. has begun b. have begunc. began d. had begun我选C24. Don’t stand up until the plane______. a. has stopped b. stoppedc. will stop d. is stopping我选C28. By the end of this month, we surely ____ a satisfactory solution to the problem.a. have found b. will be findingc. will have found d. are finding我选C 请问老师为什么错,我思路哪出现问题

回答我！55555555555555555555

,18. How long _____you ____the army till now? a. did, join b. have, joined c. have, been d. have, served in我选C 应选 d. have, served in23. The modern technology____to shrink(缩短) the distances of runways which large and fast aircraft use.a. has begun b. have begunc. began d. had begun我选C 最好用 is beginning 24. Don’t stand up until the plane______. a. has stopped b. stoppedc. will stop d. is stopping我选C 最好用 stops 28. By the end of this month, we surely ____ a satisfactory solution to the problem.a. have found b. will be findingc. will have found d. are finding我选C c. will have found

我想问思路哪出错了和为什么选这个(也就是正确答案)