某小组有3名男生和2名女生，从中任选出2名同学去参加演讲比赛，有下列4对事件：
①至少有1名男生和至少有1名女生，
②恰有1名男生和恰有2名男生，
③至少有1名男生和全是男生，
④至少有1名男生和全是女生，
其中为互斥事件的序号是______．
互斥事件是指不能同时发生的事件，
①至少有1名男生和至少有1名女生，不是互斥是件，当取出的2个人正好是1名男生和1名女生时，
这两件事同时发生了．
②恰有1名男生和恰有2名男生，这两件事不能同时发生，故是互斥事件．
③至少有1名男生和全是男生，不是互斥事件，因为“至少有1名男生”包含了“全是男生”的情况．
④至少有1名男生和全是女生，是互斥是件，因为这两件事不能同时发生．
故答案为②④．
People use their mouths for many things. They eat, talk, shout, and smile. So there are many expressions about mouth. For example, if you say things about a person, the person will be unhappy and say “Do not bad mouth me.” Sometimes, people say something to a friend or family member that later they regret they hurt that person’s feelings. The speaker might say: “ I really put my foot in my mouth this time.” If this happens, the speaker might feel down in the mouth. Information is spread through the mouth. This is general communication people, like friends talking to each other. “How did you hear about that movie?” Someone might ask. The may be : “Oh, by word of mouth.” A more official way of getting information is through a company or government mouthpiece. Sometimes, a person has a bad or unpleasant with another person. He might say: “It left a bad taste in my mouth.” Or a person might have a very experience, like being chased by an angry dog. He might say: “I had my in my mouth.” Some people have lots of money because they were into a very rich family. You might say such a person “was born with a silver spoon in his mouth. ” And this rich person is the opposite of a person who lives from hand to mouth.
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