A:what’s your future plan
B:what your future plan is
C:what was your future plan
D:what your future plan was
下列结构含有胚珠的是
如图所示,图钉尖的面积是5×10-8 m2,图钉帽的面积是1×10-4m 2,木块能承受的最大压强是6×108 Pa,手指至少要用____ N 的力,图钉尖才能进入木块。