A:充分利用物质循环和能量流动的原理,提高物质和能量的利用率
B:该大棚的所有物质和能量都能自给
C:因该生态系统缺乏分解者所以物质循环将不能正常进行
D:即使没有人的管理,该生态系统也能维持相对稳定的状态
如果a的倒数是-1,那么a2013等于( )
Hello! My name’s John. I’m in Beijing now. It’s hot in Beijing. It’s sunny too.
I can wear my shorts and shirt. My shorts are green. I have a new jacket. My old jacket is too small. I want to buy a hat.The hat is very pretty, but it is $60. that’s very expensive.
The hat is cheap.
—I'm in ____________.