A．条件(1)充分，但条件(2)不充分．
B．条件(2)充分，但条件(1)不充分．
C．条件(1)和(2)单独都不充分，但条件(1)和条件(2)联合起来充分．
D．条件(1)充分，条件(2)也充分．
E．条件(1)和(2)单独都不充分，条件(1)和条件(2)联合起来也不充分．
一元二次方程x2+(a+b+c)x+
(ac+bc+ab)=0有两个相等的实根．
(1)a=b=c． (2)a+b+c=0．
参考答案：A
解析：
考查一元二次方程根的判别式．
结论等价于
Δ=(a+b+c)2-3(ac+ab+bc)=a2+b2+c2-(ac+ab+bc)=0，显然(1)充分，如a=b=c
Δ=0．(2)不充分，如取a=b=1，c=-2，则Δ=9．
结论等价化简．
用方框中所给单词的适当形式填空，使短文通顺、正确、连贯（每个单词限用一次）。
To get the help you need, think about ___小题2:_____ to family and friends, others who also have trouble, people you meet in support groups and even help ____小题3:______. No one needs to face big trouble alone. When people in trouble look for and receive help from others , they often find it___小题4:____ to live through. You may find it hard to ask for or accept help. After all, you are used to taking care of yourself. Maybe you think that asking for help shows___小题5:_____. Or perhaps you do not want to let others know that some things are hard for you to do. All these feelings are not___小题6:_____. As one man with a great difficulty once said:“I had always been the strong one. Now I had to turn to others for help. It wasn’t easy at first,____小题7:_____ the support of others helped me get through a lot of hard times.” People feel good when they help others. Your friends may not know what to say or ___小题8:____to act when they are with you. Some people may even avoid you. But they may feel better when you ask them to cook a meal or pick up__小题9:____ child after school. There are many ways that family, friends, other people who have similar troubles and many others can help. ___小题10:____ turn, there are also ways you can help and support them! |