题目

Look! Some bread ________ in the bag and some vegetables ________ on the table. A . are; is B . are; are C . is; is D . is; are 答案：D 若平面向量a＝(1，－2)与b的夹角是180°，且|b|＝3，则b等于 [　　] A．(－3，6) B．(3，－6) C．(6，－3) D．(－6，3)