31. 關於術中監測靜脈空氣栓塞( venous air embolism)的敏感度排列，下列何者正確？ ①precordial doppler ②transesophageal echocardiography (③)end -tidal carbon dioxide ④central venous pressure (A) ①＞②＞③＞④(B)②＞③＞④＞① (C) ②＞①＞③＞④ (D) ③＞②＞①＞④