The harm the modern farming methods have done the countryside is considerable.
| A．on | B．at | C．to | D．for |
It ____ Jack twenty minutes ____ the math problem yesterday.
| A．took; to work out | B．takes; worked out |
| C．has taken; work out | D．is taking; working out |
He stood there for two hours ____ the game.
| A．watched | B．watching | C．is watching | D．was watching |
Is it always easier ____ friends than to keep them?
| A．making | B．make | C．to make | D．made |
They were made ____ fourteen hours a day.
| A．work | B．working | C．worked | D．to work |
Why not ____?
| A．let him to go home | B．to let him go home |
| C．let him go home | D．to let him to go home |