B1. We use 'can' to talk about someone’s skill or general abilities. (e.g. She can speak several languages.) And use 'can' to talk about the ability to do something at a given time in the present or future (e.g. You can make a lot of money if you are lucky.)
a. also use 'could' to say that somebody had the general ability or permission to do something. (e.g. My grandfather could speak five languages.) And use 'could' to talk about past time (e.g. She could speak several languages.)
b. can say that somebody 'is able to' do something, but 'can' is more usual. (e.g. We are able to see the lake from our bedroom window.)
c. but ‘can’ has only two forms: 'can' (present) and 'could' (past). So sometimes it is necessary to use '(be) able to'. (e.g. I haven't been able to sleep recently.)
d. We use 'could' for general ability. But if you want to say that somebody did something in a specific situation, use 'was/ were able to' or 'managed to' (not could) (e.g. The fire spread through the building quickly, but fortunately everybody was able to escape/ managed to escape. (not could))
e. The negative 'couldn't (could not)' is possible in all situation. (e.g. My grandfather couldn't swim.)
Idiom 365
Icing On The Cake: something positive (or negative) that enhances a situation that's already good (or Bad).
Example: I got a bonus from my job, and the icing on the cake was that there was no red traffic signal while I was returning home.