可以从示波器的图形上计算出被测电压或电流的幅度、周期、（）脉冲宽度及相位等参数。
A.占空比
B.大小
C.频率
D.变化关系
参考答案：C
崩塌是指堤坝临水坡在水流作用下发生的险情。其抢护原则是“（），护脚固坡，减载加邦”。
British "structuralism" linguists believed that elements in a language were ______, that is, lower level systems of word classes led to higher level systems of phrases and sentences.
A. classified B. rule-governedC. varied D. leveled
