A:It’s easier said than done.
B:He who laughs last laughs best.
C:You are trying to teach your granny how to suck eggs.
D:You can take a horse to the water but you cannot make him drink
用频率为1.00×1015Hz的紫外线照射钠的表面,释放出来的光电子的最大动能为1.86eV,求钠的光电效应极限频率.