—Whatareyoudoing  Bob? —I__________aChinesesongA.learnB.learningC

问题补充：

—What are you doing, Bob?—I __________ a Chinese songA.learnB.learningC.am learningD.am learn

答案：

C解析由问句可知答语用现在进行时，结构为：主语+be+doing,故选C。