The fire made _____ difficult to rescue the people trapped under the ruins in the earthquake.

I’ll spend half of my holiday practicing English and ________ half learning            drawing.   

“How was ______ they discovered the entrance to the underground palace？” “Totally by chance.”

The sick salesman was happy to stay at home because doing _____ was a thorough rest for him.

—Could I smoke here?—I’d prefer _______if you don’t smoke in front of the children.