蓄电池充电电压低，比重上升很慢，且有少量气泡产生，造成这一现象的原因是（）。
A.极板硫化
B.自行放电
C.极板短路
D.活性物质脱落
参考答案：C
.Professor White has received a letter ___ to give a lecture in Peking University.
A．to be invited
B．being invited
C．invited
D．inviting him
浓香型大曲酒的整个发酵过程应基本符合“前缓，中挺，后缓落”的规律。( )
