We were so excited that we rushed into t

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问题选择题

We were so excited that we rushed into the street _______ we heard the news. [ ]

A. until

B. ever since

C. as if

D. as soon as

答案

解答题

某同学进行一项闯关游戏，规则如下：游戏共三道关，闯每一道关通过，方可去闯下一道关，否则停止；同时规定第i（i=1，2，3）次闯关通过得i分，否则记0分．已知该同学每道关通过的概率都为0.8，且不受其它因素影响．

（1）求该同学恰好得3分的概率；

（2）设该同学停止闯关时所得总分为X，求随机变量X的分布列及数学期望．

单项选择题

整模造型时分型面应在模样的某个（）上

A.端面

B.截面

C.侧面