黄疸的概念。
参考答案：
由于血清中胆红素浓度升高，使皮肤、黏膜、巩膜、体液等黄染的现象，称为黄疸。
Having checked the doors were closed , and _________ all the lights were off, the boy opened the door to his bedroom.
A．why
B．that
C．when
D．where
( )是指具有独立设计文件，可单独组织施工，但是建成后不能独立发挥生产能力或工程效益的工程。
A．单项工程
B．单位工程
C．发包工程
D．分项工程
