пожалуйста раскройте скобки,и объясните почему пишется именно так!оч нужно...

1) I HAD BEEN SITTING ON THE BENCH FOR HALF AN HOUR AND THEN BEGAN READING A BOOK
2) HAVE YOU SEEN HIM THIS MORNING?-YES.HE WAS STANDING IN THE HALL LAUGHING
3 ) HE CAME IN AND SAW NELLY WAS DRAWING A STRANGE PICTURE ???
4) I DO NOT UNDERSTAND WHAT Mr Green IS DOING
. .I DID NOT UNDERSTAND WHAT Mr Green HAD DONE
5) NICK AND FRAD ARE (WERE) DRIVING ALONG THE ROAD
6) SHE WAS SETTING THE TABLE AT SIX YESTERDAY
7) THE BUSINESSMAN FLEW TO England YESTERDAY
8) I DO NOT HEAR WHAT HE IS SAYING (SAID). I AM TYPING AT THE MOMENT
9) WHEN DID IT HAPPEN?IT HAPPENED WHEN YOU WERE TALKING TO YOUR SECRETARY
10) WE HAD BEEN WALKING IN SILENCE FOR 5 MINUTES, THEN HE SPOKE
11) I TOLD HIM HE SHOULD NOT READ WHILE HE WAS EATING
12) THE MOUSE HID WHILE THE CAT WAS WATCHING

тебе нужно раскрыть скобки в Past Simple.
english.language.ru/lessons/lesson_3/grammar_3.html

1) was sitting, began
2)Have you seen, is standing
3)Came and saw
4)don't understand, is doing
5)are driving
6)Set
7)flight
8)have not hears, said, was typing
9)has it happened, happened? were talking
10) were walking, spoke
11) have told, was eating
12)was hiding, was watching
Вроде так, а почему, читай правила

Третье предложение. К чему там why?