文章中情态动词的含义与用法

2 文章中情态动词的含义与用法

You can add 10,000 hours for each decade you have lived after the age of 20.(1) Calculate for a moment what could be done with even a part of those hours. Five thousand hours，i am told, are what a typical college undergraduate spends working on a bachelor's degree. (2) In 10,000 hours you could have learnt enough to become an astronomer. (3) If it appealed to you, you could be reading Homer in the original Greek. (4) If it didn’t, you could have walked around the world and written a book about it.

1.could表示推测含义，表示推测下你利用其中的时间可以做的事情。

2.表示这已经发生的10000小时里，相当于一个含蓄条件句，“你本能如何如何”。

3.是一个表示现在时间的假设条件句，如果这时间对你来说有吸引力，你可能正读着希腊原文的荷马史诗呢。

4.错综时间条件句，分句表示现在时间，如果他对你没吸引力，主句表示过去时间，你当时可能环游世界并且写下你的记录。

请问1-4.我理解是否有误，尤其是第四句，谢谢！