由于二极管具有单向导电性，所以正向电流可以无限制地增大（）
参考答案：错
_____________ the news of the accident in the coal mine, she ____pale.
A．On hearing, got
B．At heard, changed
C．On hearing, went
D．On heard, appeared
什么是纵隔纵隔内包含哪些结构
