A:It's long.
B:It's green.
C:It's hers.
— IPhones and iPad are so popular these days.
— Yes, they can ______our eyes to the outside world.
一把大遮阳伞伞面撑开时可近似地看成是圆锥形,如图,它的母线长是2.5米,底面半径为2米,则伞面的面积是( )