Zero Conditional is used to express(a general truth или the probable future)
In the If/When-clause we usually use(Present Simple или Future Simple)
In the main clause we usually use(Present Simple или Future Simple)
In this type of conditionals, we(can или cannot) use when instead of if.
Unless means(if или if not)
When the main clause comes before the if-clause,we(use или dont use)a comma between them.
When the if-clause comes before the main clause,we(use или do not use)a comma between them.
Suddenly he (was striken) by an idea. In a moment his glass eye (was taken) out of its socket, and ( placed) on the table.
“Now, children”, he said, “I (am going) out for a few minutes but you (will be observed) all the time by my eye. If anything (is done) which (has not been approved) by me it (will be seen) by my eye, and the child (will be punished) when I (return).
The children (were impressed) very much, and the teacher (went) off.
But when he ( returned) an hour later it ( seemed) that a hurricane (had passed) through the classroom. The teacher (was astounded). “Evidently”, he thought,”I (have been outwited). I wonder how”.
In the classroom the tables (were overturned), the walls ( spattered) with ink from ink-bombs which (had been thrown) during the battle which still (was being fought) out as a manifestation of high spirits. In fact, a good time (had been had) by all.
The teacher ( wondered) why the presence of his glass eye (was not respected). He ( looked) round for it and ( saw) that it (was covered) by a hat.