真空的定义是什么？
参考答案：
真空是指气体压力低于地面上人类环境气压的状态。
给句子排队，标号。
( ) Yeah. I am tall. You're short.
( ) Wow! It's so tall.
( ) OK! Let's go!
( ) Yes. The giraffe is tall. The deer is short.
( ) Yes, it's tall. Look at the deer! It's so short.
( ) Come on, Amy. Look at the giraffe!
( 1 ) Amy! Let's go to the zoo!
假设一个生态系统的总能量为100%，按最高传递效率计算，三级消费者获得的能量为[ ]
A．8%
B．0.8%
C．0.15%
D．1%
