1. Air pollution can cause breathing problems.
$\rightarrow$ Breathing
2. Study hard or you won’t pass the exam.
$\rightarrow If$
3. I has never spoken to a foreigner before.
$\Rightarrow$ It is the first time
4. My father cleans the car every week.
– The car
5. If you don’t rest yourself, you will be ill.
$\rightarrow$ Unless
6. How long is it since he left school?
$\Rightarrow$ When
2. If you study hard, you will pass the exam.
3. It is the first time I have spoken to foreigner.
$S+is/am/are+VpII+(by+O)+….$
$Unless=If$ $not$
$\text{=How long+ is it+ since+ S+Vqk+…?}$