“Attention, please. Whoever can answer one of my questions______ receive a prize”, the teacher said in class.
___ by the advances in technology,many farmers have set up wind farms on their land.
___ many times, he finally understood it.
___ the right kind of training, these teenage soccer players may one day became the international stars.
___ not to miss the flight at 15:20, the manager set out for the airport in a hurry.
___ twice, the postman refused to deliver our letters unless we chained our dog.