薄板四周呈波浪形，说明材料中间纤维（）而四周纤维（）。锤击应由（）向（）扩散。
参考答案：短、长、中间、四周边缘
It was all my ______ that my son had made such a silly but serious _______. [ ]
A. fault; error
B. mistake; fault
C. shortcoming; mistake
D. fault; mistake
延长油田目前水处理工艺有哪些？
