“重点检重点修”的检查范围和质量标准规定：提速铁路货车钩尾扁销、钩尾扁销托及（）吊架螺母、开口销无丢失。
参考答案：安全
Sally is only eight years old, ______ she knows a lot about Chinese history.[ ]
A. and
B. but
C. because
D. so
