By the 1920s, they began to realize that what appeared as the spiral nebulae consisted of remote stellar systems millions of light-years away.是什么意思_By the 1920s, they began to realize that what appeared as the spiral nebulae consisted of remote stellar systems millions of light-years away.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句