conjunctions

Hi,

When is used if one action occurs at the same time as the other ( right ).Also, as is used in parallel actions.

This means that the following is true using either as or when,

The buses are crowded when it's wet.

The buses are crowded as it's wet.


2) In case of development actions we can use as . I wonder if when is possible?!


As the sun rose the fog dispursed.

When the sun rose the fog dispursed.


3)if we take,

As a student he had known great poverty.

What does as mean here ?.Because/ sine or while/ when and why is that ?

4) is this sentence right?,

Tired as he was he offered to carry the whole things.