在投针试验中,若l=5cm,a=20cm,则针与平行线相交的概率约为______.
针和平行线相交概率的计算公式P=2lπa=2×520π≈0.159.
故答案为:0.519.
Both of his parents died of illness so he support his family at the age of 14. [ ]
A. must
B. should
C. could
D. had to
早期即可发生淋巴转移的最常见肺癌是()
A.鳞癌
B.腺癌
C.鳞腺癌
D.小细胞癌
E.大细胞癌