But when their CD4 cell count falls below a critical threshold, they start to display symptoms of Acquired Immune Deficiency Syndrome (AIDS).是什么意思_But when their CD4 cell count falls below a critical threshold, they start to display symptoms of Acquired Immune Deficiency Syndrome (AIDS).在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句