Some physics problems in this book are _________difficult for the students _________work out.
If people change the wetlands to make space____ farms, the birds will not have enough space _____.
-Peter, did you hear any noise?-Sorry, I ________ newspapers.
Some students can’t go to the show ______ the exam this week.
________ the teachers is about 300 in our school and it is becoming_____________.
When I met Daniel at the station ______ the first time, he was in the waiting hall _____.