∵x＞1，∴x+4x-1=x-1+4x-1+1≥2(x-1)•4x-1+1=5．当且仅当x=3时取等号．
故选B．
—Hi, Lucy. Your skirt is very nice. —____
A. Yes, it’s nice. B. That’s OK. C.. Thank you.
雌激素中生物学活性最强的形式为（）
A.雌酮
B.17β-雌二醇
C.雌三醇
D.雌四醇
E.结合型雌激素
