单项选择题 男性，25岁，反复发作气促、胸闷、呼吸困难，发作时查体叩诊为过清音，两肺布满干啰音。最可能的诊断是A. 自发性气胸B. 大叶性肺炎C. 支气管哮喘D. 胸腔积液E. 肺不张

单项选择题 现代焦炉主要是（ ）焦炉 A. 倒焰式 B. 废热式 C. 蓄热式 D. 土法式

单项选择题 A researcher wants to conduct a before/after study on 11 subjects to determine if a treatment results in any difference in scores. The null hypothesis is that the average difference is zero while the alternative hypothesis is that the average difference is not zero. Scores are obtained on the subjects both before and after the treatment. After subtracting the after scores from the before scores, the average difference is calculated to be –2.40 with a sample standard deviation of 1.21. Assume that the differences are normally distributed in the population. The degrees of freedom for this test are _______.