Here comes our teacher.中here是地点副词放句首,句子倒装.英语中表示地点或方位的副词或介词短语放句首时句子全部倒装.to buy a car 在两个句子中都是不定式做目的状语,无论放句首还是放句末都是目的状语,不叫倒装句.
To find who did this is important.句中who did this 做动词find 的宾语从句,而整个不定式to find who did this 是不定式做主语,系动词是is,形容词important 做表语.