桩景材料的来源有哪些途径？
参考答案：
三大途径，一是到花木商店购买；二是自己用播种、扦插、嫁接、分株法等培养；三是到山野挖掘野生老树桩再行加工
Jenny is on holiday now. I wonder ______________________.
A．when she will come back
B．when she came back
C．when will she come back
D．when did she come back
负责维护交通安全、交通秩序，进行交通管理、处理交通事故的警察称为交通警察。( )
