【单选题】中药材生产关系到中药的质量和临床疗效。关于中药材种植和产地初加工管理的说法,错误的是( )
C.
对野生或半野生药用动植物的采集应坚持“最大持续产量”原则
【简答题】若调制信号为v Ω =V Ω cosΩt,载波为v c =V c cosω c t,如下图所示。写出调频信号的表达式v FM ,写出瞬时频偏ω(t),瞬时相偏φ(t)的表达式。
【单选题】There was something wrong with the network, or the email ________ earlier.
【单选题】----Where is Tom? ----He’s left a(n) _____ saying that he has something important to do.