Two old men were playing chess in the park with trees ________ shade.
A:providing
B:provided
C:to provide
D:provide
ATP之所以能作为能量的直接来源,是因为( )
如图所示,通电螺线管附近的小磁针处于静止状态,则螺线管A端是 ____ 极,电源的D端是 ____极.
“坐地日行八万里,巡天遥看一千河”诗中的“地”所在的纬线是( )