расчитать массовую долю серы в соединениях ZnS

помогите пожалуйста поставить глаголы в правильное прошедшее время:

6.  It (be) more than a month before I (realize) what (happen).

7.  When Jack (not/arrive) by 6p.m. I (know) he (miss) the bus.

8.  When I (meet) him he (work) as a plumber for a year or so.

9.  We scarcely (start) eating when there (be) another scream.

10.  We (look) through the agreement before we (sign) it.

11.  I (be) very pleased when my son (find) my watch because we (look) for it for hours.

12.  Nina (think) she (leave) her purse in a locker in the changing room the day before.

13.  I (wake) up and (look) out of the window. Everything (be) white. It (snow) all night.

14.  Not until I (look) at my watch did I realize how much time (pass).

15.  Karen (admit) that she (make) a mistake and (apologize).

16.  Isabel (send) a postcard to the girl she (make) friends with while she (attend) a language course.

17.  They (run) out of petrol because Paul (use) the car se­veral times before.

18.  When we (get) to the airport we (hear) that they (cancel) all the flights.

19.  When our teacher (see) what Tom (do) she (be) absolu­tely furious.

20.  My old watch (work) very well for many years before I (drop) it.

21.  I (run) out of money but luckily I (be) able to borrow enough to get home.

22.  I (have) to be early the next morning, so I (excuse) myself and (leave) the party.

23.  He (keep) his job although the manager (threaten) to sack him several times.

24.  When Mr Gabb (come) out of the water, he (find) that somebody (take) all his clothes.

25.  After the movie (finish) they (decide) to get something to eat.

26.  Many modern medicines were not invented by western scientists but by tribal people who (use) them for gene­rations before Europeans (arrive).

27.  It was not surprising that she (start) getting a bad tooth­ache. She (not/go) to the dentist for two years.

28.  Her work (look) really neat because she (use) the computer.

29.  The chairman's main fault was that he persistently (interrupt) the speakers before they (finish).

30. After she (dress) and (eat) her breakfast, Linda (rush) off to her office for a meeting with her accountant.

31 Peter already (see) that musical before he (read) the re­view about it.

32.  When I (go) into the room I could smell cigarette smoke. Obviously somebody (smoke) in there.

Закончите предложение (Принцип,положенный в основу первой научной классификации живых организмов называется.....)

Автобус проезжает расстояние между двумя городами за 30 часов. Если автобус и легковая машина одновременно выедут из этих городов навстречу друг другу то они встретятся через 12 часов. за Сколько часов расстояние между городами проезжает легковая машина.