(a) Как Вы уже заметили, since и for часто употребляются в предложениях с Present Perfect Continuous. Мы используем since для указания момента начала действия:

- She has been watching TV since early morning.

- They have been travelling since last Monday.

For употребляется для указания всего периода времени:

- He has been working in that firm for two months.

- It has been raining for 3 hours.

- They have been agruing about that for more than an hour.

Но с выражениями

all day all morning all week all my life..

НИКОГДА НЕ УПОТРЕБЛЯЕТСЯ for.

- It has been raining all day long.

- She has been training all week long.

(b) Используйте Present perfect (I have done/I have been doing), чтобы спросить или сказать, как долго (how long) что-то происходит (до настоящего момента). Помните структуру How long is it since...?:

- It's two years since I saw your flat.

- It's ages since we visited this place.

- How long has it been raining?

- It's been raining since one o'clock.

(c) Обратите внимание, что с when всегда употребляется Past Indefinite Tense (I did), не зависимо от того, спрашиваете ли вы что-либо или говорите:

- When did he come home?

- When did you see this film?

- He was preparing for his report, when the telephone rang.

- When I entered the room I saw my mother sitting in the armchair.

(d) Помните конструкцию How long is it since?

- It’s two years since I saw your flat.

- It’s ages since we visited this place.