我访问了亚洲和非洲仍然流行脊髓灰质炎的四个国家，以亲眼观察正在作出的巨大努力，而这些努力往往是在极其困难的条件下作出的。
I have visited each of the four remaining polio-endemic countries, in Asia and Africa, to observe first-hand the tremendous efforts being undertaken, often under very challenging conditions.
在后续的医生访问和检验中，观察等待成本只有几千美元。
Watchful waiting costs just a few thousand dollars, in follow-up doctor visits and tests.
DBA必须知道如何通过观察EXPLAIN结果来检查和定位访问计划中的问题。
It is important for a DBA to understand how to look at EXPLAIN output to detect and locate problems in the access plan.
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