在植物体内合成生长素较集中的部位是
①顶芽 ②茎的形成层 ③幼嫩的种子 ④根尖分生区[ ]
A．①
B．①②
C．①②③
D．①②③④
答案：D
A．电磁铁的上端为N极，小磁铁的下端为N极
B．电磁铁的上端为S极，小磁铁的下端为S极
C．电磁铁的上端为N极，小磁铁的下端为S极
D．电磁铁的上端为S极，小磁铁的下端为N极
. I told your friend how to get to the hotel, but perhaps I __________ have driven her there.
A．could
B．must
C．might
D．should
