【单选题】The attitude of the Federal Bureau of Investigation shows that ______.
A.
enough data are yet to be collected from various ethnic groups to confirm the unlikelihood of two DNA samples coming from two individual members
B.
enough data of DNA samples should be collected to confirm that only DNA samples from the same person can match
C.
enough data are yet to be collected from various ethnic groups to determine the likelihood of two different DNA samples coming from the same person
D.
additional samples from various ethnic groups should be collected to determine that two DNA samples are unlikely to come from the same person 61. The National Academy of Sciences holds the stance that ______ .
【简答题】课本习题1-12: 在一次测定空气横向流过单根圆管的对流传热试验中,得到下列数据:管壁平均温度 t w =69 °C,空气温度 t f =20 °C,管子外径 d=14mm ,加热段长 80mm ,输入加热段的功率为 8.5W 。 如果全部热量通过对流传热传给空气,试问此时的对流传热表面传热系数多大?