A:However life is difficult
B: However is life difficult
C:However difficult life i
D: However difficult is life
光线从一种透明物体进入另一种透明物体时,传播方向会在交界面上发生弯折,这种现象叫____。
甲试管:经高温煮沸冷却后的豆浆;
乙试管:人体必需的8种氨基酸溶液;
丙试管:蛋清和蛋白酶;
丁试管:人血液中的红细胞和蒸馏水
对于平行线,一定要在____范畴内研究。