从2008年6月1日起,我国就禁止生产、销售、使用超薄塑料购物袋.下列对聚乙烯塑料叙述不正确的是( )
2013年,太仓市实现地区生产总值1002.28亿元,用科学记数法表示1002.28亿元为____元.(保留2个有效数学)
已知在直角坐标系xOy中,直线l的参数方程为 {x=1+tcosαy=tsinα(t为参数,0<α<π2) ,若以O为极点,x轴正半轴为极轴建立极坐标系,曲线C的极坐标方程为ρcos2θ+4cosθ=ρ(ρ≥0,0≤θ≤2π).
(Ⅰ)当 α=π3 时,求直线l的普通方程;
(Ⅱ)若直线l与曲线C相交A,B两点.求证: OA→⋅OB→ 是定值.
根据表格内容, 选择正确答案。
(B)
Wang Wei
I can't sing or dance. I can play the guitar. But I couldn't play it three years ago.
Alice
I can sing and dance. I can also play the piano. When I was six, I couldn't play the piano at all.
James
I can swim and cook. I can't draw pictures. I could swim when I was five years old.
Liu Fang
I can perform ballet and dance to disco. I can also sing English songs. But I couldn't sing English songs two years ago.