信号的作用是保证（）与（）的安全，提高列车通过能力。
参考答案：列车运行、调车作业
So loudly _____ that ____ hear her clearly.
A．did she speak; could everyone
B．did she speak; everyone could
C．she spoke; could everyone
D．she spoke; everyone could
固定化细胞发酵的优点?
