配制一种盐水，盐和水的重量比是1：2，盐是盐水重量的______．
1÷（1+2）=13．
故答案为：13．
— Linda hasn't shown up yet.
— It's strange. She _____.[ ]
A. could
B. might
C. must have
D. should have
春季角结膜炎分为________、________、________三型。
