搜题请搜索小程序“爱下问搜题”
问题 选择题
已知mx2+mx+m＜1的解集为R，则m的取值范围是（　　）
A．（-∞，0）B．(-∞，0)∪(
4
3
，+∞)		C．（-∞，0]D．(-∞，0]∪[
4
3
，+∞)
答案

①当m=0时，mx2+mx+m＜1化为0＜1，其解集为R，满足条件；

②当m≠0时，要使mx2+mx+m-1＜0的解集为R，必须满足

m＜0
△=m2-4m(m-1)＜0
，解得m＜0．

综上可知：m的取值范围是（-∞，0]．

故选C．

选择题

可用于电动汽车的铝--空气燃料电池，通常以NaCl溶液或NaOH溶液为电解液，铝合金为负极，空气电极为正极。下列说法正确的是 [ ]

A．以NaCl溶液或NaOH溶液为电解液时，正极反应都为：O2+2H2O+4e-=4OH-     

B．以NaOH溶液为电解液时，负极反应为Al+3OH- - 3e-=Al(OH)3↓     

C．以NaOH溶液为电解液时，电池在工作过程中电解液的pH保持不变     

D．电池工作时，电子通过外电路从正极流向负极

查看答案
单项选择题

Fred Heyach and Gord Murdoll are discussing whether or not competitive markets use resources efficiently. Heyach says, "Competition must lead to the efficient allocation of resources. Consumers are willing to pay more for the goods they want most, so producers of those goods can outbid other producers for the resources to make them. Murdoll replies, "At any one point in time the market might allocate resources efficiently given consumers’ preferences, but as consumers change their minds about which goods they want, the allocation of resources becomes inefficient. " Are these statements correct or incorrect Heyach Murdoll （） ①A. Correct Incorrect ②B. IncorrectCorrect ③C. IncorrectIncorrect

A. ①

B. ②

C. ③
查看答案