若P(2,-1)为圆(x-1)2+y2=25的弦AB的中点,则直线AB的方程是()。
A. x-y-3=0
B. 2x+y-3=0
C. x+y-1=0
D. 2x-y-5=0
E. A、B、C、D都不正确
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She shows little regard for the feelings of others and does exactly what she wants to().
A. feeling
B. love
C. consideration
D. sense
-- Must I finish it before 10 o'clock -- No, you().
A. mustn't
B. needn't
C. can't
D. don't
小麦为异源六倍体作物,其x=7。所以他的单体系列可以有______种类型。
A. 42
B. 28
C. 21
D. 7
某种氨基酸由二个以上密码进行编码,这种现象是______。
A. 简并
B. 复制
C. 转录
D. 翻译