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问题 填空题
连掷两次骰子得到的点数分别为m和n，若记向量
a
=（m，n）与向量
b
=(1，-2)的夹角为θ，则θ为锐角的概率是______．
答案

设连掷两次骰子得到的点数记为（m n），其结果有36种情况，若向量

a
=（m，n）

与向量

b
=(1，-2)的夹角θ为锐角，则
m-2m＞0
-2m-n≠0
，满足这个条件的有6种情况，

所以θ为锐角的概率是

1
6
，

故答案为

1
6
．

单项选择题

无菌区对洁净度要求是

A．大于10万级
B．10万级
C．大于1万级
D．1万级
E．100级
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问答题

What’s your earliest memory Do you remember learning to walk The birth of a sibling Nursery school Adults rarely remember events from much before kindergarten, just as children younger than 3 or 4 seldom recall any specific experiences (as distinct from general knowledge). Psychologists have floated all sorts of explanations for this “childhood amnesia”. The reductionists appealed to the neurological, arguing that the hippocampus, the brain region responsible for forming memories, doesn’t mature until about the age of 2. But the reigning theory holds that since adults do not think like children, they cannot access childhood memories. Adults are struck with grown-up “schema”, the bare bones of narratives. (46)When they riffle through the mental filing cabinet in search of fragments of childhood memories to hang on this narrative skeleton, according to this theory, they don’t find any that fit. It’s like trying to find the French word in an English index.
Now psychologist Katherine Nelson of the City University of New York offers a new explanation for childhood amnesia. (47)She argues that children don’t even form lasting, long-term memories of personal experiences until they learn to use someone else’s description of those experiences to turn their own short-term, fleeting recollections into permanent memories. In other words, children have to talk about their experiences and hear others talk about them — hear Mom recount that days’ trip to the dinosaur museum, hear Dad re- member aloud their trip to the amusement park.
Why should memory depend so heavily on narrative Nelson marshals evidence that the mind structures remembrances that way. (48)Children whose mothers talk about the day’s activities as they wind down toward bedtime, for instance, remember more of the day’s special events than do children whose mothers don’t offer this novelistic framework. Talking about an event in a narrative way helps a child remember it. (49)And learning to structure memories as a long-running narrative, Nelson suggests, is the key to a permanent “autobiographical memory”, the specific remembrances that form one’s life story. (What you had for lunch yesterday isn’t part of it; what you ate on your first date with your future spouse may be.)
Language, of course, is the key to such a narrative. Children learn to engage in talk about the past. The establishment of these memories is related to the experience of talking to other people about them. (50)In particular, a child must recognize that a retelling — of that museum trip, say — is just the trip itself in another medium, that of speech rather than experience. That doesn’t happen until the child is perhaps four or five. By the time she’s ready for kindergarten she’ll remember all sorts of things. And she may even, by then, have learned’ not to blurt them out in public.
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