一个襟翼手柄位置对应一个襟缝翼形态，除了（）
A、位置1
B、位置2
C、位置3
参考答案：A
________ at failing in the maths exam, John wouldn't like to talk about it to his parents.[ ]
A. Disappointed
B. To be disappointed
C. Disappointing
D. Having disappointed
产业结构主要从哪几个对象进行优化？
