Perhaps you should try some spelling variations:
"improving basic performance series." » "improving basic performance studies.", "improving basic performance size.", "improving based performance series.", "improving music performance series.", "improving baseline performance series.", "improving air performance series.", "improve basic performance series."
"improving basic performance risk." » "improving based performance risk.", "improving music performance risk.", "improving baseline performance risk.", "improving basic performance 2019.", "improving air performance risk.", "improve basic performance risk."

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• Performing a fuzzy search may retrieve terms with similar spellings: (("improving basic performance series.") or ("improving basic performance risk."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving basic performance series.") OR ("improving basic performance risk.")).
• Removing quotes may allow a broader search: (( improving basic performance series. ) or ( improving basic performance risk. )).
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