_____ of the students who took part in the military training is 450.
---Is he here now?---No, I ___ he ___ here by now.
My brother tried ___, but still he couldn't work out this maths problem.
He seemed as if he ___ his homework when his mother came in.
The poster says that a writer and poet ___ to give us a talk on English next week.
How this kind of plant can be ____ in a special way is still unknown to us.