植物组织培养的基本步骤
参考答案：
（1）培养材料的采集
（2）培养材料的消毒
（3）制备外植体
（4）接种和培养
（5）根的诱导
（6）组织苗的练苗移栽
.I was about to leave_________I saw him_______ towards me, with a bag in hand.
A．while; running
B．when; running
C．as; ran
D．when; to run
