原发性腹膜后肿瘤的发生区域包括（）
A.肾前旁间隙
B.肾周间隙
C.肾后旁间隙
D.中线大血管周围区域
E.小网膜囊
参考答案：A, B, C, D
---Where is Zhang Ming?
---Oh, don’t you know he to Beijing to see his parents and he’ll be back tomorrow.
A. has gone B. has been C. had gone
如图①～④列举了四种作物的育种方法，请回答相应问题：
①代表的育种方法是（）。
