湖泊生态系统在结构上可分为三个层，即浅水层、______、深水层。
参考答案：表水层
— Excuse me, may I start right now?
— ________.[ ]
A. It's none of my business
B. You have got it
C. Sure, go ahead.
D. It's your turn
6个月～6岁小儿血红蛋白正常值的低限是
A．80g/L
B．90g/L
C．100g/L
D．110g/L
E．120g/L
