选用下列词的适当形式填空: sound sight thought invitation loss requirement risk suggestion expense knowledge service 1) At the ____________ of the coming examination the boy felt very nervous. 2) He paid a visit to their home for drinks at the _________ of the newly-married couple. 3) At the _________ of the gun the birds in the tree flew away in all directions. 4) He hesitated at the _______ of her face suggesting her disagreement with his plan. 5) At the ___________ of the doctor he takes regular exercise to keep fit. 6) He built up a successful business but it was all done at the __________ of his health. 7) At the ___________ of the bus conductor all the passengers showed their tickets. 8) We rescued more than 50 children at the ______ of our lives. 9) A good salesman is never at a _______ for words. 10) My telephone is at your _________ until yours is repaired. 11) Altough he is young, he has a great appetite for __________ of economics.