many extra-curricular useful book 要多作课外的练习题 ; 多积累词汇 ; 多看课外有用的书
It has many omissions; even so, it is quite a useful reference book.
那本书有许多遗漏之处，即使如此，尚不失为一本有用的参考书。
But integrating your existing online social connections could be useful for many of Apple's products, ranging from the iPhone's address book to the App Store to photo sharing.
但是集成现有的社交连接对于许多苹果的产品(如iPhone的地址簿、应用商店、照片分享等)肯定是非常有用的。
Putting in a simple timeline, for instance, would have been more useful than the introduction, which devotes many pages to detailing what will be said in the rest of the book.
他的编辑看来是个懒人，比如，加入一条简单的时间线将比浪费很多页来细述这本书接下来会讲什么的引言更有用。
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