Ктеме "условные предложения" ,нужно раскрыть скобки.1 the child ( not to be) healthy if you (not to give) him much fruit 2/ if i (i not to be i present at the lession, i ( hot to understand) this difficult rule 3. you would have understand the rule if you (not to miss) the teacher"s explanation

1the child won't be healthy if you don't give him much fruit.
2if I am not present at the lesson I won't understand this difficult rule.
3You would have understood the rule
if you hadn't missed the teacher's explanation.

The child would not be healthy if you didn't give him much fruit(hadn't given тоже может быть - но подразумевалось тогда бы в а здоров он сейчас). If I hadn't been present at the lesson I wouldn't understand this rule. You would have understood ( или wouldn't understand - потому, что сейчас человек не понимает правило) the rule of you hadn't missed the teacher's explanation