高氟地区斑釉牙和氟骨症多发,低氟地区龋齿多发,这种现象称为()
A.统计性地方病
B.自然疫源性地方病
C.聚集性地方病
D.化学元素性地方病
E.输入性地方病
参考答案:D
—Is that your pencil?
—______. That is her pencil. [ ]
A. Yes, it is
B. No, it is
C. No, it isn't
D. Yes, it isn't
焦炭的热值是3×107J/kg,完全燃烧2kg的焦炭放出的热量为____________J。