单项选择题

铅对婴幼儿危害更大，吸收率高达______________。
A、10%
B、100%
C、30-50%
D、50-70%

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4、差模电压增益Ad是指_与_之比值

答案：差模输出电压，差模输入电压

多项选择题

How can teachers deal with stduents' individual differences?
A. Teachers' can deal with students' differences spontaneously

B. A lesson plan should take into account the variation of ability in students

C. Don't judge students on their differences

D. Design and give effective individual counseling