一 Have these workers finished doing their work ?
— No, not .
A:already; yet
B:yet; yet
C:yet; already
D:already; already
—I can see ____ bags.
P是△ABC所在平面上一点,满足PA→+PB→+PC→=2AB→,若S△ABC=12,则△PAB的面积为( )
如图为探究“磁生电”的实验装置。