阅读理解
    Different weather makes people feel different．It influences health，intelligence and feelings．
    In August，it is very hot and wet in the south the US．People there have heart trouble and other kinds of health problems during this month．In the Northeast and the Middle West，it is very hot in the summer and very cold in the winter．People in these states have more heart trouble after the weather changes in February or March．
    The weather can also influence intelligence ． For example，in a 1983report by scientists，IQ(智商)of a group of students was very high when a very strong wind came, but after the strong wind,
    Their IQ was 10% lower than before. The wind can help people have higher intelligence. However,very hot weather can make it lower. Students in many schools of the US often get worse in exams(考试)in the hot months of the year(July and August).
    Weather also has a strong influence on people's feelings．Winter may be a bad time for thin people．They usually feel cold during these months．They might feel unhappy during cold weather．But fat people may have a hard time in hot summer．At about 18℃people become stronger．Low air pressure may make people forgetful．People leave more bags on buses and in shops on low-pressure days．
    Are you feeling sad，tired，forgetful，or unhappy today？It may be the weather's problem．

下列关于功、功率和机械效率的说法中，正确的是（   ）

春秋时期，我国农业发展史上的一次革命是指（    ）

大圆周长是小圆周长的2倍，大圆面积是小圆面积的（ ）倍．

有关此符号中3$\stackrel{+6}{S}{O}_{4^{2-}}$叙述不正确的是（　　）