A:15×107
B:1.5×108
C:1.5×109
D:0.15×109
____
给出命题:“若x2+y2=0,则x=y=0”,在它的逆命题、否命题、逆否命题中,真命题的个数是( )
意义:赤壁之战为____局面的形成奠定了基础。
Can you see the boys football on the playground? They are my classmates.