糖类按其组成一般可分为（）三大类。
A．冰糖、麦芽糖、葡萄糖
B．葡萄糖、果糖、蔗糖
C．单糖、双糖、多糖
D．麦芽糖、蔗糖、乳糖
参考答案：C
把R1=5Ω，R2=15Ω串联起来，则串联后的总电阻为（ ）
A．小于5Ω
B．20Ω
C．15Ω
D．5Ω
My mother is busy ________ the meat because she wants to ________ dumplings for us.[ ]
A. cutting off, make
B. cutting down, made
C. cutting up, make
D. cutting up, made
