读一读,选择正确的答案,将字母代号写入前面的括号内。
① Is he nine? ____ A. Yes, I am.
② Are you a boy?____ B. I'm a cow.
③ Are you two? ____ C. I'm four.
④ How old is your sister? ____ D. She is ten.
⑤ Who are you?____ E. Yes, he is.
食物链、食物网是生态系统的营养结构,生态系统的物质循环和能量流动是沿着此渠道进行的.假如在某温带草原上存在如图所示的食物网.请分析回答:
为预防骨质疏松症,可适量补充含钙的无机盐和( )