MODALS & PERFECT MODALS
It's impossible that he knew the problem ---- HE ............. THE PROBLEM
HE CAN'T HAVE KNOWN THE PROBLEM
We have bought more food than was necessary for the party ---- WE _______ FOR THE PARTY.
WE NEEDN'T HAVE BOUGHT MORE FOOD FOR THE PARTY.
I'm sure they didn't phone you --- THEY __________ YOU.
THEY CAN'T HAVE PHONED YOU.