—Who is the old man talking with your teacher?—I don’t know. I _________ him before.
You can't imagine what great fun my brother and I had _________ up and down the tall, shaky steps.
—I find the environment is getting worse and worse. —Yes, that is _________ we humans go against nature.
The famous painter _________ birds kept in cages in order to have the pleasure of setting them free.
While intelligent people can often simplify the complex, a fool is more _________ to complicate the simple.
When I _________ the past and think how much time has been wasted, my heart bleeds.