Which of the following statements best describes the property of the system T if y1（t）=T[x1（t）], y2（t）= T[x2（t）] implies T[ax1（t-s）+bx2（t-s）]= ay1（t-s）+by2（t-s）（）

A. the system is linear

B. it is a linear time-invariant system

C. the system satisfies the principle of superposition

D. the system satisfies additivity and time-invariance