将编号为1，2，3，4的四个材质和大小都相同的球，随机放入编号为1，2，3，4的四个盒子中，每个盒子放一个球，ξ表示球的编号与所放入盒子的编号正好相同的个数．

（Ⅰ）求1号球恰好落入1号盒子的概率；

（Ⅱ）求ξ的分布列和数学期望Eξ．

A.Lessenthechanceofgettingcancer

B.createanidealobservationcondition

C.ensurecitizensagoodsleepatnight

D.enableallcreaturestoliveinharmony

A.Psychologiststhinksatisfyingworkiskeytohappiness

B.Psychologists'opinioniswellprovedbyGrandma'scase

C.Grandmaoftenfoundtimeforsocialgatherings

D.Grandma'shappinesscamefrommodestexpectationsoflife

A.Savingwildlifeissavingourselves

B.Greateffortsshouldbemadetosaveenergy

C.Humanactivitiesshouldbeenvironmentallyfriendly

D.Newequipmentshouldbeintroducedforspacestudy

A.Happinessliesbetweenthepositiveandthenegative

B.achmanisthemasterofhisownfate

C.Successleadstohappiness

D.Happyishewhoiscontent

A.Shecareslittleaboutherownhealth

B.Sheenjoysthefreedomoftraveling

C.Sheiseasilypleasedbythingsindailylife

D.Sheprefersgettingpleasurefromhousework