三角形木架的形状不会改变,而四边形木架的形状会改变,这说明三角形具有( ),而四边形不具有( ).
稳定性,稳定性。
—Would you like to go shopping with this afternoon?
—I'd love to, but my mother is sick. I _______ look after her at home. [ ]
A. can
B. may
C. could
D. have to
锯电缆以前,应与电缆走向图图纸核对相符,并使用专用仪器(如感应法)确切证实电缆无电后,方可工作。