赞题库-背景图

单项选择题

Which of the following descriptions was true about Zheng Hes voyage? A、Zheng He made seven westbound voyages. B、For Ming Dynasty, Zheng Hes voyage is unsuccessful. C、Zheng Hes voyages ranged 30 years. D、Zheng Hes fleet traveled to more than 28 countries.

<上一题目录下一题>

热门试题

单项选择题衡量汽轮发电机组工作完善程度的指标是（）。

A.绝对电效率
B.相对电效率
C.相对内效率
D.循环热效率

单项选择题由凝汽器变工况特性知：当排汽量下降时，真空将（）。

A.提高
B.降低
C.不变