题目

—How long _____ at this job? — Since 1990. A . were you employed B . have you been employed C . had you been employed D . will you be employed 答案：B如图甲所示为一种调光型台灯，通过旋动下方连接碳膜电阻的旋钮，就可以调节灯的亮度．调节亮度的电路如图乙所示，P为旋片，可随意转动从而改变在碳膜上的位置．要将图乙连在图丙所示的电路中，要求顺时针旋转旋片可以使灯泡亮度增加，下面接法正确的是（　　）A．A 接M，B 接NB．A 接M，C 接NC．C 接M，A 接ND．C 接M，B 接N