下面的英语句子有没有翻译错误，有没有语法短语的错误，或跟好的表达方式??请大家，帮忙纠正。

This is a secret between you and me, don't tell anyone.
It is really a good idea to travel by train if you don't like to travel in a hurry.
Hanan Island is the second largest island in China.
Could you tell me how long it took him to write this book?
或者：
Could you tell me how long he spent (in) writing this book?
其实任何一种语言都有比较灵活的表达，只是看你强调什么了。
很高兴为你解答！
老师祝你学习进步！
望采纳，多谢你的问题！^_^

这是你和我之间的秘密，不要告诉任何人。
This is the secret between you and me.Don't tell anyone.
对孩子们来说，在动物园里观看各种各样的动物是很有趣的，对吗？
For children, It is very interesting to watch all kinds of animals in the zoo, right?
如果你不喜欢匆匆忙忙的旅行，坐火车旅行真是个不错的主意。
It is a good idea to travel by train ,If you don't like traveling in a hurry .
海南岛是中国第二大岛。
Hainan island is the second largest island in China.
你能告诉我写这本书花了他多长时间吗？
Could you tell me How much time he spent (in) writing this book?

最后一句 Could you tell me how much time he spent in writing the book?

我认为最后一句应改为Could you tell me how long he spent in writing the book?