发电机同期并列操作可采用（）和（）两种方式，正常情况下，应选用（）方式。
参考答案：自动准同期；手动准同期；自动准同期
输煤系统信号装置包括？
Tests provide grades, but they also let you know what you need to spend more time（）and they help make your new knowledge permanent.
A.to study
B.study
C.studied
D.studying
