单选题Collecting stamps as a&nb

问题补充：

单选题Collectingstampsasahobby___________increasinglypopularduringthepastfiftyyears.A.becomesB.becameC.has becomeD.had become

答案：

C解析主语collecting stamps as a hobby被看成是整体，谓语动词用第三人称单数形式。而时间状语during the part fifty years限制了句子用完成时态。