构成安全健康的办公室环境的基本要素有：空气、光线、声音、空间、__________五种。
参考答案：绿化
采油指数的单位是（）。
At what gestational age would a primigravida expect to feel "quickening"（）
A. 12 weeks.
B. 16 to 18 weeks.
C. 20 to 22 weeks.
D. By the end of the 26th week.
