Everyone knows that ______ is dangerous to play with fire, but ______ is difficult is to prevent children from playing with fire.
I asked him ___ it, but he just remained unmoved.
Although he didn't expect ___ me here, he adviced ___ to the nearest resturant.
He had learnd ___ such things, so he refused ___.
In the complete darkness, she began ___ afraid.
John had ___ me to do this, but he didn't .