A:胚珠外有无果皮包被
B:种子外有无子房壁包被
C:种子外有无果皮包被
D:种子的有无
—When shall we go hiking again?
—Make it _____day you like. It's all the same to me.
设NA为阿伏加德罗常数的数值,下列说法正确的是( )