Teachers in low-income urban and rural areas with nohistoryof participating in math competitions may not know about advanced-math opportunities like Math Counts.
低收入的城乡地区的教师没有参加过数学竞赛，他们可能不知道有像 Math Counts 这样学习高数的机会。
3
The man had nohistoryof travel during the month prior to symptom onset.