為甚麼要用for 跟 the？

She hates to wait...她討厭等...。不定詞to wait（屬不及物用法，無受詞）當動詞hate的受詞。
for the bus是用來修飾上面這句的「不定詞」to waitt。for xxx 表示「目的」：為了XXX。
名詞bus是可數名詞，單數時，通常要在前面加上「不定冠詞」a（＝ any one），或「定冠詞」the（= that one）。I will go there by bus.這時才不用冠詞（指的是方法: by taking a bus）。當說話的人說She hates to wait for the bus.時，心目中對bus的類型是有指定的，即是指「那種為公共用途而有固定路線的」交通工具。而且聽者也能意會說者所指的是那一類型的交通工具。

"the" is not used with uncountable or plural nouns when you mean "all"of something in general=not specific.
eg:-We ride the bus,watch the video,drank the beer.
"wait for" is the idiom=used to tell to do something until the correct time, because she seems very impatient to do (the waiting for the bus) now !