【单选题】
非单位负反馈系统,其前向通道传递函数为G(S),反馈通道传递函数为H(S),当输入信号为R(S),则从输入端定义的误差E(S)为()
①
<imgwidth="126"height="22"src="../uploadfiles/word/zdkzll002.files/image040.png">
②
<imgwidth="169"height="22"src="../uploadfiles/word/zdkzll002.files/image041.png">
③
<imgwidth="176"height="22"src="../uploadfiles/word/zdkzll002.files/image042.png">
④
<imgwidth="168"height="22"src="../uploadfiles/word/zdkzll002.files/image043.png">