—I think buyers________ spend too much time going to shops.
A:needn't
B:mustn't
C:can't
D:shouldn't
已知正项等比数列{an}的公比q=2,若存在两项am,an,使得aman=4a1,则1m+1n的最小值为____
甲、乙两台机器分别灌装每瓶质量为500克的矿泉水.从甲、乙灌装的矿泉水中分别随机抽取了30瓶,测算得它们实际质量的方差是:S甲2=4.8,S乙2=3.6.那么____ (填“甲”或“乙”)灌装的矿泉水质量较稳定.
设a>0,b>0.若 3 是3a与3b的等比中项,则 1a+1b 的最小值为( )