交换机运行软件系统结构，从功能上可分为哪三大部份？
参考答案：操作系统、数据库系统和应用软件系统
—Mrs. Wang was sent to teach English in a poor mountain village last year.
—She said she would never forget some pleasant _______ while working there. [ ]
A. experiments
B. expressions
C. experiences
D. emotions
发生骨转移最多见于下列哪种恶性肿瘤？（）
A.甲状腺癌
B.肺癌
C.肾癌
D.前列腺癌
E.乳腺癌
