磷硅玻璃是有()组成。
A.CF4
B.SiO2
C.磷
D.SiF4
参考答案:B, C
观察下列各式
(x-1)(x+1)=x2-1
(x-1)(x2+x+1)=x3-1
(x-1)(x3+x2+x+1)=x4-1
…
(1)分解因式:x5-1=______;
(2)根据规律可得(x-1)(xn-1+…+x+1)=______(其中n为正整数);
(3)计算:(3-1)(350+349+348+…+32+3+1);
(4)计算:(-2)1999+(-2)1998+(-2)1997+…+(-2)3+(-2)2+(-2)+1.
— He ought ot have been warned of the danger.
— ____, but he wouldn't listen to me. [ ]
A. Yes, he ought to
B. So he was
C. So was he
D. So it was with him