一 Nowadays most young people _____ sending short messages ____ notes.
一 After all, science is developing faster and faster.
A:preferred; to write
B:prefer; to writing
C:preferred; to writing
D:prefers; writing
英国曼彻斯村经过100多年,变成了工业城市,生活在那里的桦尺蛾也由浅色品种多变成了深色品种,原因是( )
读图,判断下列叙述正确的是( )
已知x>0,y>0,且4x+1x+y+9y=26,则函数F(x,y)=4x+y的最大值与最小值的差为( )