to no avail的用法和樣例：
例句
- His intervention was of no avail.
他的調停無效。 - His claim to ownership is invalid.
他的所有權是無效的。 - This is a subject into which many scientists have researched with no result.
這是一個雖經很多科學家研究過但尚無結果的課題。 - Seven patients had abnormal urinalysis but no positive finding in culture.
七位病人之尿液常規檢查顯示白血球增多但培養無結果。
