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.
He ______ his uniform every day. It’s _______ beautiful.
A.wears , kinds
B.wears, kinds of
C.in , kind of
D.wears, kind of
下列动物中体内有脊柱的是( ) ①家鸽②藏羚羊③蚯蚓④鲫鱼⑤蟾蜍⑥蝗虫.
A.①②④⑤
B.①②⑤⑥
C.①②③⑤
D.①②④⑥