A:经济迅速发展和城市化水平提高
B:人口自然增长率下降和生活水平提高
C:平均寿命延长和人口自然增长率上升
D:环境质量改善和人口素质提高
试剂/种类
碘液
苏丹Ⅲ染液
双缩脲试剂
甲
++++
++
+
乙
丙
Today David is busy doing his homework. So he has no time ____ (play) computer games.