Saving the earth（The Fifth Period）

        hardly had i arrived when i had a new problem to cope with.
        no until all the fish died in the river did the villagers realize how
        serious the problem was.
        so fast does light travel that it is difficult for us to imagine its
        speed.
  note: in all these sentences, inversion happens in the main clause, not in the   subordinate clause.
4. when “only” is used to modify an adverbial which is placed at the beginningof the sentence.
  e. g. only in this way can you succeed.
        only then did i realize that i was wrong.
  note: when “only” is used for emphasis of a subject, normal word-order is
          used.
  e. g. only john knows the answer.
5. in some special forms of unreal conditional clauses, when “if” is left out,  the structure “were (should, had) i (you/he ,etc)” are used instead of “if  i (you/he, etc.) were (should, had)”.that is to say, inversion can be used
  instead of “if”.
  e.g. were he (= if he were)  here now ,could ask him.
       should he (= if he should)
       come, tell him to ring me up.
       had you (= if you had )  not helped me, i’d have failed.
  note: if there's no：“were” “had” or“should”in the unreal conditional
    clauses, inversion can't be used.
 6. in questions
    e. g. have you seen john?
    note: inversion is not always used in questions. like the following cases:    (1) in a special question, if the subject is expressed or modified by an
interrogative word ,the subject comes before the predicate.
        e. g. what happened to mary?
              how many people are listening to the lecture?
   (2)in some other cases:
        e. g. you've seen john?           
              i wondered whether he'd seen john.
7. in sentences expressing “blessing” or“concession”.