Nowhere in nature is aluminum found free, owing to its always ____ with other elements, most commonly with oxygen.
A、beingcombinedA
【句意】由于铝总是和其它元素结合在一起，最常见的是和氧气在一起，所以自然界中哪里也不会找到单独的铝元素。
【难点】owingto是介词，后应接名词或动名词，根据题意，应接被动语态形式。
Ithappenedinfrontofafruitandvegetable____inmyneighborhood.
Dr.Yangworked______threedaysago.
Theoldmanlivesinavillage_______,butheneverfeels________.
Whentheideaofwinninginsportsiscarriedtoexcess,____competitioncanturnintodisorderandviolence.
Physicsisthepresentdayequivalentof____usedtobecallednaturalphilosophy,from____mostofpresentdaysciencearose.
