How much do you remember about this subject?
For and since are commonly used with the present perfect tense.
We use for to talk about a period of time.
E.g. "I haven't smoked for weeks."
We use since to talk about a specific point in time, or a time when the action started.
E.g. "I haven't smoked since 2010."
It can be quite tricky to know which one to use and just like everything else, you need to practise!
In the following sentences, should you use 'for' or 'since'.