He ... not buy lunch because he didn't have any money. (ability)
could (was NOT able To buy)
You ... take my pen if you need. (permission)
can
I ... speak 2 foreign languages.(ability)
can
My friend ... call me when he needs. (permission)
may
All my friends ... (invite) to my party. (permission)
can be invited
... I use your phone? (permission)
Can (Could/May)
I ... do my homework. (duty/rule)
must (have TO)
She ... drink at least 2 litres of water a day. (advice)
should (ought to/has to)
If you want to pass your test, you ... revise more.(advice,duty)
should (have to,must.need to)
He ... call the doctor. (advice)
should (has to)
We ... to buy bread because we have 2 loaves at home. (advice)
don't need (needn't buy)
In the future I ... speak Chinese fluently. (ability)
will be able to
In my childhood I ... not swim. (ability)
could (was NOT able to)
All children ... study at school. (rule)
must
Children ... play less video games. (advice)
should (ought to)
Please .. I use your laptop? (permission)
can (could)