化灰池的四周应设围栏，其高度不得小于1.2m，并设（）。
参考答案：安全标志牌
The salesman showed her several MP3s and she chose ________ one as she didn't want to spend too much money on it.
A．the less expensive
B．less expensive
C．the least expensive
D．least expensive
对排卵起关键作用的激素为
A．前列腺素
B．催乳激素
C．黄体生成素
D．雌激素
E．雄激素
