=3= It is...that..已经是强调句啦.
是Light travels in straight lines is known to all.的强调句.
如果对你有所帮助,还望采纳哈!
如还有不懂的,还可以继续追问哦\(^o^)/~第一个是强调句，It是形式主语，
light travels in straight lines是真正的主语
is known to是谓语
all 是宾语
第二个是时间状语从句the plane是主语is to take off是谓语has not been announced是宾语 这两句的句子成分划分的对吗