单项选择题 建成以来，该桥经受了多次洪水和地震，但其主体结构仍然完好无损，至今仍在使用。 Since the completion, the bridge has withstood floods and earthquakes, but remains intact in its main  structure and still available in use.  Since  the bridge was completed, the bridge has withstood floods and earthquakes, but its main structure  remains intact,  used until now. The first English sentence is a better translation. A、正确 B、错误

问答题 单相全桥逆变电路移相调压方式的工作原理？

单项选择题 双因素方差有交互项的，比如有自变量a和b，则交互项就是a*b，如果a*b项显著，也就是其p值（即sig）小于0.05，可以认为交互作用显著。（ ）