Our maths teacher set so difficult an examination problem ______ none of us worked out.
In that school, German is compulsory for all students, but English and French are_______.
.After the earthquake, the first thing the local government did was to provide ____________for the homeless families.
It is reported that North Korea once agreed to _________its neclear program in exchange for economic aid and security guarantees.
The students are warned not to talk about anything ______ to the accident that happened the other day in the school.
The river have ________, so they will have to spend much money irrigating(灌溉) the crops.