训练球主要用于（）
A.肌肉松弛
B.平衡训练
C.综合基本动作训练
D.训练下肢肌力
E.训练上肢肌力
参考答案：A, B, C
---What do you think of the film called So Young?
--- I think this is the most wonderful film _______ I have ever seen.
A．that
B．who
C．whom
D．what
试述引起多道程序系统程序执行不确定性的内部原因？
