单选题 The doctors are at a loss because so far no medicine has been found to______the spread of the disease.

单选题 He knows that the______of social status can consume vast amount of his time and efforts.

单选题 Most cities in the country have introduced "Clean Air Zones"______factories and households are only allowed to burn smokeless fuel.

单选题 People there are told it is their______duty to support the national economy by buying their own products.

单选题 Darwin's thinking both drew upon and______the conventional ideas of his time.

单选题 We see many special education directors trying to______the quality of their programs.

单选题 My advice to Mr. Stewart is to think carefully before entering into a career in medicine, as this field which requires a lot of______and long working hours.

单选题 In spite of all your______, there may be times when you encounter difficulties in the training process.