生物进化的总体趋势是:由简单到复杂,由低等到高等,由胎生到卵生.
抛物线 y=x2−2x+m2+2 (m是常数)的顶点在 ( )
A. fold the clothes B. sweep the floor
C. make your bed D. take out the rubbish
E.do the dishes
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