Most appropriate for indexes are sites (or parts of sites) that do not change too frequently, that have repeat users, and that have rich and varied content.

最适合使用索引的网站是那些不经常变化的，有常客访问，有丰富的和各种各样的内容的网站。

youdao

PointsHound says that it gives more generous rewards to repeat users.

BBC: New ways to earn miles faster

If a search engine can provide consumers with the newest, freshest links from the social web in a way that makes sense, they will undoubtedly attract repeat users.

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The 33 million figure Pincus quoted may then have been the number of unique, rather than repeat, users.

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