If you don't know how to spell new words , ______ in the dictionary.       [ ]

A. look up them    

B. look for them    

C. look them up      

D. look them for

下列实例中，属于能够遗传的变异的是

A．经常锻炼的人肌肉发达

B．经常在野外工作的人皮肤变黑

C．豌豆的茎有高茎和矮茎

D．小花生种到肥沃的土壤中长成大花生