E. As = at the same time as. The structure of the sentence is usually: as + subject + verb (e.g. Nobody sings as she does.)
a. You can use ‘as’ when two things happen at the same time. (e.g. We all waved goodbye to Ann as she drove away.)
b. also use just as (= exactly at that moment) (e.g. Just as I sat down, the phone rang.)
c. use of as is to say what the role/function of a person/thing is. (e.g. He started work as a carpenter.)
E1. Because is more common than as and since, both in writing and speaking. When we use because, we are focusing on the reason. (e.g. She spoke quietly because she didn’t want Catherine to hear.)
a. We often put the because-clause at the beginning of a sentence, especially when we want to give extra focus to the reason. We use a comma after the because-clause. (e.g. Because breathing is something we do automatically, we rarely think about it.)
E2. We often use as and since when we want to focus more on the result than the reason. As and since are more formal than because. We usually put a comma before since after the main clause. (e.g. They’re rather expensive, since they’re quite hard to find.)
a. We often use as and since clauses at the beginning of the sentence. We use a comma after the as- or since- clause. (e.g. Since everything can be done from home with computers and telephones, there’s no need to dress up for work anymore.)
b. We use because, not as or since, in questions where the speaker proposes a reason. (e.g. Are you feeling unwell because you ate too much?)